I think part of what diotalevi is saying is true... but not the part about there being no competition. I know that some people (myself included) do sometimes play the game of Who can be the first to give a good answer to a new question. It's true that the First Responder (:-) tends to get an XP advantage, at least when there are significant numbers of voters out there; but there's also something intangible that accrues to the First Responder. I think it is akin to how status is gained in the hacker world. (See also The Hacker Milieu as Gift Culture.)