Yeah, this can't be called an "ulterior" motive. It's just... the motive. What else would they be trying to do?
But... yeah, I wish I could be happier about this. While I hate Live's ethics and am extremely happy to see somebody offering competition (and seeming like a much better deal entirely, hopefully smashing it to bits), I wish that competition was something I could support. Unfortunately, I hate Steam quite a bit more than Live, sooo... yeah. Fuck.