Apple is probably even more likely to lock their users down to using their app store only and taking a 30% cut is than Microsoft is. That's an "out of the frying pan into the fire" solution.

With Linux, Valve has the control. If they were getting really serious with this, I'd expect them to take full control over the hardware they're selling too, but for the moment, this is still a pretty solid BATNA-threat for them.