I'm not really in the know, but I've seen that a whole lot of people have been playing the Day Z mod for ArmA 2 very recently, and suddenly ArmA 2 pops back up on Steams top sellers.
http://www.youtube.com/watch?v=A7Q8c8jnL3s
That can't be a coincidence, right?
Also, is it any good? It's certainly got my interest.