What up with Netflix?

Well I'm new to Netflix and don't know much about it. So I've been watching "Dexter" on Netflix lately, and I noticed that it said something like "streaming available until 7/1/11", and now they've taken the series off Netflix. I was wondering why that is and if they're going to put it back. Also, I noticed that there were only 2 seasons of "Dexter" loaded on there when there are actually 6 seasons. Are other series like that? And why aren't all of the episodes loaded on there? Thanks.