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.
