Put it this way, Steam is the lesser of evils when it comes to PC DRM these days. I'm very grateful they didn't use Windows Live.
I hate all forms of DRM.
So, dawnguard won't be available to PC on a disc? Like in a shop? Cos, well, I ain't buying from Steam. I like to support my local game store, not many going these days. (I mean like a family run business, no companies or anything, they can support themselves well enough without my input.)
Reason is, my mum ran a game shop, and I'd rather support families than mega corps. Sometimes have to wait a little longer for special orders but it's worth it to me.