Earlier quoted context omitted.
What are you basing this on? The quote in both the linked article and the AllThingsD piece indicates that he said "I think Windows 8 is a catastrophe for everyone in the PC space." He isn't just talking about Valve.
A business catastrophe, not a usability or market catastrophe. "I think margins will be destroyed for a bunch of people."
On the other hand, Microsoft's new 20-30% cut doesn't sound like very low-margin distribution infrastructure either...