Not to diminish Carmack's significance and genius, but, from waht I can tell from the first minutes of the interview, he knew he was going to be awarded, so je had plenty of time to prepare and rehearse his -- very inspiring, I should say -- speech.
For something like a decade (2004~2005 until 2013), Carmack gave a fluent hours-long speech/discussion/brain-dump at QuakeCon. I doubt a few minutes's speech is something he needs "plenty of time to prepare and rehearse" for at this point.
Carmack's talks are mind-blowing, he just talks off the cuff fluently for two-three hours and it's consistently interesting, it's completely insane. Here's one he gave at SMU in 2014: https://www.youtube.com/watch?v=fOzkUKJCxTw
Even with prep writing a speech that good isn't easy. Easier sure, but that's like the difference between a high wire act and a high wire act with bears waiting to eat your corpse.
That's fair, but I'm willing to bet that anyone who has a chance of receiving an award is well-prepared to give a speech. Executing the speech is difficult whether you are ready or not, and Carmack not only spoke well/fluently, but had a great message that was meaningful because it came from him and also, because it can resonate with anyone really.
What a hero! Very excited to see the innovations coming out of VR/AR over the next few years.