I don't use the other SE sites much, at leat not the technical ones, but if they are anything like my experience with many other forums it's very common to see multiple people offering the same answer. This is particularly common where there is some reward on offer for providing answers, in the guise of reputation points or whatever. I don't personally see this as a good thing, as people will often reply to the questions directly without checking to see if someone has already provided the same answer as you. This is as bad to me as the OP not googling what should be a simple questions.
I'm not sure what the etiquette is on the other sites, or if I do things wrongly on here, but if I see an interesting question, and find that it has already been substantively answered along the lines of what I might have said, I won't bother with replying, but would just upvote the existing reply. This might explain the lower answer rate on here, but not the lower vote rate (if this really exists, surely someone can provide metrics to prove it's not just anecdotal).
As for questions, I generally upvote ones that I can't answer and would like to know the answer to, even if it's just out of curiosity, but if it's something either daft, duplicate, simple or just plain edge case and of little interest to me, I won't upvote it, even if it's perfectly valid for the OP and meets the site rules.
Overall, I would hazard a guess that the users of this site are generally just a little less interested in ego stroking, and vote on a stricter criteria, and as such are voted on by like minded posters. I don't care about my score, but I do like it when I have an answer accepted, even if no-one else upvotes it.