I love reading other people's responses on a fic and if everyone started using polls there would be nothing to read.

You could always read the fic itself. ;) But in all seriousness, I don't think it's going to catch on. I think many writers would be afraid of how it might make them appear (begging for comments, needy, desperate for feedback, etc.) even if as readers they appreciate the option.

Oh man Triceratops! Hard to beat three horns and a head that had to have weighed at least a ton.