Yes, the primary function of the answer questions is help, but polls don't allow you to give the detailed answers you might want to give to some answer questions. As for forums, great as they are, hardly anyone bothers with them compared to some of Fanpop's other features! Probably because they never show up in the updates.

It depends. If it's something that provides a detailed answer or something that has an incredible amount of choices, you can do Answers, but if it's just something like, "X VS Y?" It belongs in polls.

I'm not sure why some people do it but it doesn't bother me.

Some questions just don't work well in poll format. They could require long complicated answers, or there are too many answer options to list them all, or it could be asking for something like a hierarchy.