I would just say they've been paying attention to valve and are copying it.
http://www.techdirt.com/articles/20090219/1124433835.shtml
It's like valve says. Pirates are nothing but underserved customers.
It's just customers finally getting around to doing things intellegently.
Provide a killer game like TF2, then additional items that can be earned or bought in a shop... and you end up making huge ROI for a small amount of staff. Even more so when you liscence out a lot of the modeling to your own fan community offering them a slice of the pie.