Impulse isn't Steam, for the record. Just to point out, Steam came out in 2003, and didn't come out with the "Steam Community" until 2007. That means no steam friends list, no ingame browser, no outside friends list you can use as an IM program, etc. Impulse isn't even a year old. Some of these features are being worked on in Demigod, like the ability to PM other players, join their games, create clans, etc., but you can't expect a brand-new content delivery system to be as full-featured as one that's six years old.
In case you don't believe me:
http://en.wikipedia.org/wiki/Steam_(content_delivery)
and
http://en.wikipedia.org/wiki/Impulse_(content_delivery)