At the moment, in a small private beta with relatively low voting rates, your question makes sense. Even popular questions get few votes, so whether or not the answerer votes up makes a big difference. However, I see this as a short term phenomenon that won't be worth thinking about beyond private beta.
If a question is good enough that it is getting votes from viewers, then the answerer's vote will not make a significant difference. If a question is getting very few votes from viewers, then that suggests it is not a great question, and the answerer shouldn't feel obliged to upvote.
I think the answerer should choose whether to vote and whether to answer as two separate decisions. In most cases where I post an answer, it is because I found the question interesting, and so I upvote. I wouldn't want to be pressured to upvote though, or conversely pressured not to answer if I don't feel like upvoting.
There may be cases where a question is not off topic and there is no reason to close it, but it is not a particularly good question. Adding an answer that demonstrates the problems with the question and explains why there can be no definitive conclusions can be helpful for future reference, and if I saw such a situation I would upvote the answer but not the question.