Is there any logical basis for the practice of a user answering a question but not upvoting the same question? It seems to me that if you answer a question, then it implies that you believe it meets the criteria for the site. So, why wouldn't you upvote it? Likewise, if you don't believe it meets the criteria, you wouldn't bother answering it, and you might also downvote it.
Voting on questions has little or nothing to do with whether questions meet the criteria of the site. That consideration is more relevant to the Vote to Close mechanism. Posts that don't meet the criteria for the site should be closed—whether up-voted or down-voted.
The factors you consider when using each function of the site should be as logically separated as possible. Sometimes you may upvote questions you answer, sometimes you may even downvote them. As I recently brought up on the C.SE meta you might even vote to close and upvote a question or answer it and downvote it.
There are lots of factors that go into voting on questions, but the relative quality, perceived usefulness, and many other things might play into it. Meanwhile choosing to answer or not could include very different factors.
That's not to say that enough people vote on questions. Looking at the voting statistics it's pretty clear a lot of people are reading posts and even posting while barely ever voting. This isn't a good thing as the voting system works better the more people are active. The more people regularly up and down vote posts the more effective a system or ranking content it becomes. Personally I try to vote on every post I read one way or another. Sometimes for very mediocre posts with no great pluses and no stand out negatives I end up split between the pros and cons and end up figuring +1/-1 is no vote, but I always go through the quick mental exercise of figuring out what direction to vote and why.
Are you asking this because I answered this question of yours without upvoting it?
You have edited it slightly since the time I answered (nothing of consequence), but I did not upvote it because I did not think it was good enough to merit an upvote (I also did not downvote it because I did not think it was bad enough to merit a downvote).
One reason I did not cast an upvote is because your question did seem somewhat silly. You quoted Matthew's and Mark's account, and then when Luke relates almost the exact same details of Jesus' baptism, such as
- heaven opening
- the Holy Spirit descending on Jesus as a dove
- and a voice from heaven saying "You are my beloved Son..."
you seemed to convey that since Luke does not specifically write the word "John" in vv21-22, John could not have baptized Jesus and this was a different event.
Another reason was that Luke only mentions one person baptizing people in chapter 3: John. Verse 21 begins with "Now when all the people were baptized...", most of that chapter is focusing on John, and since you yourself quoted Matthew and Mark already, who else would Jesus have been baptized by?
It appeared that you were nitpicking, and this kind of nitpicking is actually a pet peeve of mine. I've also read some of your answers to other questions, and they are quite good and very detailed, and deal with complicated subject matter, and I do remembering thinking when I first read your question, "Why is this guy, of all people, asking this? He should be the one answering this type of question instead of asking it!"
All of these things taken together are why I did not upvote your question.