He's showing that people were aware, that Greenhouse was removed, because 94 people voted on the poll were this was stated. So if anyone cared enough the change his vote, they had the chance.
And while I do agree some people might have voted differently if Greenhouse was out of the picture from the start, it probably wouldn't have changed the outcome of this poll. The winning abilities both have atleast a 20+ votes advantage and that's too much to disregard, just because some may have voted differently. Especially after people already had the change to chance their vote. Don't forget this was a bold poll, so if someone only voted on say Rock Head, because of Greenhouse, they could've changed their vote when Greenhouse was removed. Everyone had the opportunity to change their vote, not just the Greenhouse voters. So there's no need for another poll just to give a few people, that were to late with their change, another chance.
Also, if anyone wanted the weather project, but still have Greenhouse on Woodman, he or she could have said so. But I don't believe anyone did.