If it were about the app store, why does Gabe have nothing to say about the Mac App Store?
In my poking around on this, I saw plenty of assertions that this was all about the app store, but nothing is ever attributed to Newell except his lament that the usability is off and the sales aren't there.
Because Mac and iOS gaming doesn't represent such a large share of their business. The doom and gloom doesn't make sense otherwise, Steam functions perfectly well on Windows 8, as do all other desktop, non-"Modern UI" apps, so there's no other conceivable reason for him to get irate.
> "The doom and gloom doesn't make sense otherwise"
But the 'doom and gloom', from Gabe's mouth, doesn't seem to be any more extreme than his stated position on DX10/Vista. As far as I can find, the press are the ones taking his comments to extremes, reading into them about app stores, etc.