I can't imagine Valve putting in the time/effort to get Steamworks on PS3 just so Portal 2 can update itself. The only reason I can see for adding Steamworks to the equation is as the prelude for a major Valve presence on PS3.
It's clear that Valve initially favoured MS& Live until it became clear MS only wanted their games and had no interest in allowing Valve to penetrate their own digital gaming infrastructure. I doubt they're swinging this effort behind PS3 - and Gabe basically eating crow in public on a platform - just for Portal 2.
However it was agreed Sony have clearly decided to share their PSN infrastructure with Valve's Steamworks for Valve titles - and I'm very interested to see where that goes post Portal 2.
Of course, Portal 2 selling well on PS3 would help.
Try to be reasonable... its easier than you think...
