Well, as VALVe is the sole company working on it, I don't see any problem with them making it a steam exclusive, just as I don't have a problem with Stardock making their products Impulse exclusive...
Exactly. I, for one, am looking forward to Portal 2. Some of its so-called 'new features' were the selling point of an independant game I played a while ago, involving using a paint gun to naviagte levels (green paint makes you jump, blue paint makes you walk on walls, etc.)