Slightly Devil’s Advocate here: I’m 99% certain vBulletin let you edit them post creation/vote, and I’m fairly certain phpBB and most of the other players do too. I believe their intent is, if you edit it in such a way, you’ve destroyed your own ability to use the data (so it ends up being meaningless); which ultimately gives you more reason to not edit it in a way that would make the data meaningless (if you actually care about the results).
I’m at the point, I won’t use the poll feature in Discourse. It is too cumbersome for me to want to use for the rare number of times I actually need/want one. So I just create one elsewhere and link to it… 
(works for me, but sort of defeats the purpose of having it internally). Just my experience.