It's IMO wise to treat comments from people like Carmack and Gabe with a bucketload of salt.
Gabe is just a Microsoft-era millionaire and behaves as such in support of Microsoft. Valve may not have much technical knowhow amongst its team as they always relied heavily on 3rd party middleware game engines to base their games on.
Carmack has been proven to spout propaganda for Microsoft as well. He even once claimed Doom couldn't be done on the Amiga, but of course as soon as the source code was made available a few days later Doom ran on older Amigas than same age top PCs could.