We should also encourage good comment, since not everyone is willing to write a long detailed answer, they may provide thoughts which is also very important. Also comment is the start of a deeper discussion, so I think we should encourage a little bit of good comment by giving some reputation to the corresponding person who writes a voted up comment.
Imagine the loss of some great points by the some people who may think the question is not worthwhile to write an answer, or they are too busy or too lazy to do so.