Its on steam!
http://store.steampowered.com/app/20920/
Yeah, and is the case with most games on Steam: it costs more for less content.
I'll be getting a boxed copy with some interesting pre-order content for £5-10 less than if I bought on Steam, and installing on the same day. And if it's fucked I can return it and get a refund without getting my entire library locked away from me.