I worry that it will go the other way and Steam will have to charge more to compete with Origin and it's growing list of exclusives. The pricing plan for The Old Republic doesn't exactly bode well for us the consumer if EA gains a lot of ground.
One thing I would add is that even without support from other publishers, EA has an impressive list of franchises that it could make Origin-exclusive, I know that I will be using the service for things like Battlefield, the next Mass Effect, Dragon Age, Mirror's Edge and Dead Space titles ect. They will probably have most gamers using the service next year and from then making exclusive deals with other publishers will probably entice enough people into buying from them. Not that I think Steam is circling the drain, I just think that Origin actually can be a serious rival in a short (year or two?) kind of time-frame.