Re: just liking a thing versus having to talk about why you like a thing, I remember reading about a study about that a while ago that I can't find now, but it concluded that people would choose a different thing when they were told beforehand that they would have to explain why they chose the thing, and deliberately chose things they could explain well instead of what they actually liked.
This is about the same thing: http://en.wikipedia.org/wiki/Introspection_illusion#Attitude_change, the last paragraph kind of sums it up.