True, you can setup the polls and question to reduce the problems but they are all still there since you still asking the user rather than measuring the actual behavior.

I.e., polls are a form of proxy for what you really want to learn but can't get directly. Your example of voting polls is a great example of this... Until the actual election, we can't know and so polling is about as good as we can get. (But I won't even bother to mention all of the games that are played with the polling to manipulate the outcomes. :-( )