The biggest change for 2013 is that microsoft is throwing PC gaming under the bus and trying to move all gaming to the consoles. Evidence, you want evidence:

1. Gaben and a bunch of other people says it's true (http://www.eurogamer.net/articles/2012-11-06-gabe-newell-rig...)

2. MS is no longer supporting cross platform (xbox/pc) development and is killing XNA. (http://www.extremetech.com/gaming/147289-microsoft-kills-xbo...)

Also steam supporting linux has significantly increased the number of linux games. Android linux compatibility is a big win for casual games on linux.