There's a Meta.StackOverflowMeta.StackOverflow question about rate-limitations, which also links to this MSO questionthis MSO question on accepting an answer which explains it's pretty much to give other users chance to post an answer - if you see a question with the green tick of acceptance it's less likely that they'll post another answer.
replaced http://meta.stackexchange.com/ with https://meta.stackexchange.com/