The whole upvote thing is like a freemarket concept to ideas. I guess if enough people decide to upvote something even though it isn't interesting (to them) then it will be more likely to reduce the quality of the front page if we all share the same idea on what is interesting or not... which is I guess the point of voting and having a community of like minded individuals.

Personally, I don't think people would sustain upvoting things they don't like.