This is related to, but not a duplicate of, this question.
There are many times when I see an good and/or accepted answer, and I start to upvote it, but then I stop because it already has more upvotes than seems appropriate, given the quality/difficulty of the answer. There's nothing wrong with the answer, but it doesn't seem like it's earned 10 upvotes when it probably only took them 2 minutes.
Is that wrong? Are there any official criteria for what's worthy of an upvote (other than "This answer is useful")?