What he says holds great weight in the industry simply because without him, we'd all probably still be playing 2d games.
No, we'd still have 3d games without John Carmack. But technology would likely be a year or two later... JC's genius has helped the game devs by bringing practical, fast 3d techniques to the market quicker than they otherwise would have been. Without him, these excellent techniques may have been discovered later (if at all), and we would likely be waiting longer for Moore's law to give us enough horsepower to play equivalent games since 3d graphics may not have been as efficient.
So Far Cry could have been last year's release, rather than 3 years ago.
Three dimensional games would have happened without John and id. There have been many 3d engines made over the years that did not use any of Carmack's innovations. They were often slower than engines built upon his techniques, but they worked. 3d gaming would have existed, but we likely would not have had a superstar programming god leading the way.
Dreaming Demon, formerly Tikatt, formerly The Raven