If both MS (and Apple) got their act together, Steam would be in trouble. They are both pushing online stores which eventually they'll probably get right.
It makes sense for steam to try to get into the under-the-telly position before Apple and MS do. Neither of those two are just in the OS business anymore so steam can't rely on not having its undelying platform competing with it. It would be good to have always-on ARM system coupled with a more powerful PC.
That said, +1 for next HL 3