Happy birthday!
Gabe himself and other members of Valve have stated they are never having games be platform exclusive to Steam Box. They said thats against what Valve is all about. So if Half Life 3, Portal 3, or L4D3 ever come out. They wont be exclusive.
Due to rumors and job listings, its been more or less confirmed both Visceral Games and Bioware are working on Star Wars games thanks to EA's new contract with Disney to create Star Wars games