We talked about the Steam stuff on the podcast (episode 15 I think). I had a feeling they would do it like that. It's a bummer since I might have pre-ordered it on Steam to get the Signature Edition, but it's really just business on EA's end. Steam is such a powerhouse in the digital distribution world and helping out the other services (e.g. Impulse, D2D, GamersGate) builds better business relationships with them. You can say they're screwing their Steam customers, but I for one know that I'm going to buy DA2 during one of Steam's many ridiculous sales for like $25 and spend (considerably less than) the difference on DLC.
TL;DR It's not very nice for Steam users, but I'm not going to hold it against them since I'm going to buy it on sale anyway.