I think it was ported to X360 from PC. Still guessing, but that's just the impression I got.

I thought it was the other way round, usually is, these days.

Turns out it's one of the few games that are made for 2 platforms at the same time, similar to Unreal Tournament 3.

Update: Edit actually uses Unreal Engine 3 so it's maybe, probably, not so much of a surprise.

Necrobump.

I just bought this in the Steam sale for £12.74. Much better than the £55 it used to be.

Left 4 Dead.