I work at Best Buy, so take what I'm about to say with a grain of salt.
Tablets can never replace laptops though.
Hm? I wouldn't say that! It's all about context, honestly.
Most consumers that walk in the door have needs that mirror the criteria listed in the OP. The only other common requirement is word processing capabilities, and
Microsoft Office 365 supports Ipads and Windows-based tablets. With Windows-based tablets like the
Lenovo Yoga 2 and the
Asus Transformer T100TAM running the full Windows 8.1 OS (eliminating software-related compatibility issues & app-based limitations - not that the Microsoft Store doesn't still kinda suck), in addition to USB ports (in the T100TAM's case, which is especially useful for peripherals like
external optical drives), microSD card slots for data transfer/memory expansion,
HDMI output, bluetooth capabilities, and 1080p displays, tablets are, for all intents and purposes, perfectly capable of replacing laptops for a lot of people. The two of them even have great battery lives and come with the keyboard already in the box!
And that's only from looking at lower end stuff. Microsoft's Surface Pro 3 is a full-fledged laptop disguised as a tablet, and the only mobile devices carried in store that are actually capable of outperforming it are the ones accompanied by dedicated GPUs (like the
Lenovo Yoga Thinkpad 14 or the
15" Macbook Pro) for gaming & 3-D rendering-related needs. The Surface Pro 3 has been so ridiculously successful that
Dell and
HP have each released their own laptop/tablet hybrids with M Processors & full SSDs in hopes of competing. They don't have the 8.1 PRO OS, and aren't (as) optimized for/accompanied by a stylus, but they are significantly cheaper and the keyboard is already in the box, so you don't have to spend $130 dollars just to have something to type on and cover up the screen with. They're honestly the coolest things I've seen HP and Dell make in a long time and I can't wait to see what other companies come up with.
Anyways. I'm rambling.
The point is: tablets are more than capable of replacing laptops. For a lot of people, they already have, and for individuals that need the portability & battery life of a tablet combined with the power offered by a laptop, well, they've already got plenty of options. With all of that said:
Any tablet will do given your vague generic needs.
Soul Fly totally hit the nail on the head. There is honestly not a single tablet (I've seen) incapable of satisfying the needs you'be outlined by the OP. If you haven't already, I highly recommend walking into a Best Buy and hunting down and Apple and Samsung representative (assuming a store close to you has one). They'll know their products front to back, can help you better navigate/take advantage of what their respective OS's offer, and help you decide if you really care about any of their unique bells and whistles. Blue Shirts will know their stuff too, but the reps are probably a better resource when it comes to the more intimate questions. I did a little bit of research while I was at work the other day, so I'm gonna try and help you out as well.
Looking at Apple, the
iPad Mini 2 is probably the most cost effective option available. They can be bought as cheaply as $250.00 (open box/refurbished), and the only things offered by the iPad Mini 3 are a better camera, the thumbprint id thing, and higher storage capacities. The former two don't really matter, while the latter is gotten around via iCloud. If you don't like the cloud, though, a Dropbox app is available, too. If you plan on purchasing a keyboard-case for it, Office 365 has OneDrive - Microsoft's version of Dropbox/iCloud - and comes with a license for 1 PC/Mac & 1 Tablet, so you can do you schoolwork while your out and about. You could probably use Google Docs for the same thing since it lets you export stuff as Word documents, but that's only as reliable as your internet connection.
The iPad Air is another viable option, but the only thing it has over the iPad Mini is a larger screen - and 7" is plenty big as is! I recently bought my little sister (and by proxy, the rest of my family, since they seem to be using it just as much) an iPad Mini 2 for Christmas and I was pretty shocked about how large it felt. Demonstrations are usually done within arm's reach since the iPad's Retina Display means you don't have to hold it close to your face to actually see what's going on, and this can make it seem small. But when you're actually lying down with it on the couch, or in bed, I've found it more than large enough. Definitely ask yourself how big you'll need it to be.
If you like the iPad Air's size, I'd also look at the
Samsung Galaxy Tab S, since it's within the same price range. I was playing with the demo and the AMOLED display is absolutely brilliant - much better than Apple's Retina Display, I think (and it's already pretty fantastic). The videos on the demo were movie theatre quality (though, I might be overselling it just a tad). Anyways, if you plan on consuming a lot of media & feel more comfortable using SD cards rather than iCloud/Drop Box/One Drive, Samsung's Galaxy Tab S has an incredible display and can have
2.25x the amount of physical storage offered by the iPad Air 2 at the same price.
Keyboards can be pretty pricey depending on who you buy it from (not that this is any different for the iPad) but price matching* and open box items** can help mitigate costs. Office 365 doesn't support Android-based tablets, though, and Google Docs is only as reliable as your internet connection. Their app store might have something that makes this a non-issue, however, if such a thing were a concern.
*Best Buy price matches competitors like Amazon & Newegg as long as it's shipped and sold by them. The Galaxy Tab S is
$50.99 cheaper on Amazon than it is at Best Buy. Don't be afraid to do a little digging, 'cause it's definitely more convenient than paying shipping & waiting for it to arrive to just pick it up in store.
**Open box items are a great way to save some money since defective products aren't resold and customers usually return them because they didn't like it or couldn't get it to work, not because there was actually anything wrong with it. I don't know if the Best Buy website only tells you what's available in your area (since the damn thing won't let me log out), but it's available for as low as $399.99 on my end. Definitely consider this when you're shopping around, especially if other vendors offer similar deals.
Although their app store isn't as well supported, there are some pretty interesting Window-based tablets available that'll be significantly less expensive than the above.
The
Lenovo Yoga 2 & the
Asus Transformer Pad T100AM both offer 1080p resolutions, HDMI output, microSD card support, come with the keyboard already in the box, and run the full Windows 8.1 OS, eliminating software-related compatibility issues. Although the Lenovo Yoga 2 doesn't have USB ports like the Asus Transformer, it does have a higher resolution, and the hole in the kickstand lets you hang it up, giving it some rather dynamic uses that other tablets can't offer. The loss of USB means you can't use flash drives, optical drives, hubs, docking stations, external hard drives, or
wireless mice with it, though (unless they're 100% bluetooth). None of this may matter, however, as you already have a fully-functioning laptop. You might find the ability to carry these around in place of your laptop an appealing possibility, though.
Anyways, that's just my two cents! I'm not familiar with everything that's available as I mostly with laptops/desktops, not tablets, but these guys stood out from what we carry at my store.
I think Macle might have the right idea, and I'll try to explain why when I get back from work.
Good luck!