To be fair Steam wasn't either, in the beginning, which also ruins my argument wrt the iTMS quite a bit: even the Orange Box was still a retail product to most (it's even in the name!) that just happened to be consumed through Steam. Not much different from how iPod users had to use the client app for CDs bought in retail (or far more likely: mp3 from the Napster substitute du jour)

You couldn't download even blizzard games through battle net until 2013. Steam's first third party games were in 2005. They're not really comparable.