Valve released Counter-Strike: Global Offensive just this August. They've also been putting a lot of resources into DOTA 2, and are probably fairly close (ie: within three months) to releasing it after a ridiculously long beta period.
Okay I'll admit I forgot about CS:GO, just goes to show how big an impact that game made on me given that I totally forgot it existed, even then Valve doesn't exactly have a schedule choke full of must have games. CS:GO is still being out played by it's much much older CS Source and CS brothers.
DOTA2 on the other hand does seem to be racking up the numbers but what degree is Valve involved in that? Didn't they just hire the guys who made it, in which case, Valve being Valve the only folk who are working on it are the folk who have always been working on it, would explain why it has been in Beta for so long.
Saying that still doesn't explain why Valve are wasting time on Steam for Linux and augmented reality hardware.