Though I agree with most answers and comments (and the general idea behind not linking comments and votes down) I also can't agree with the question.
What about people with a really high reputation and really bad day? Minus two for votedown is absolutely no penalty for them. How do you want to track down that someone voted down ten or twenty times a day, just to give himself a little bit relief of frustration?
This (current) situation is a specially painful, in a "conflict" of people with a really low reputation (like me) asking question and giving answers, that gets votedown virtually by no reason. This doesn't happened (yet) to me, but just a minutes ago I saw a few answers to few PHP questions, a really good answers, that were voted down for no reason and of course, without any explanation.
Is there anyone out there, that thinks similarly to me, that people with small reputation, after being voted down to many reasons at the beginning of their journey with StackOverflow, will simple resign from contributing?
SO is really big. I've been using much smaller contribution systems up until now. But must of them, after a period of feeding questions like this with similar answers, like here, ended up with introducing system that requires a comment to vote done. Simply, because it isn't fair to get vote down without reason and without any explanation.