I think this is a sign that the Xbox One specs might be potentially better than the PS4. Why else would Carmack address this? Is it because of all the hardware comparisons? I personally don't think so. If they are essentially the same, I guess all that boils down to is the library of games. Personally, I think the Xbox One will win now since their exclusives are pretty good, but you can't deny the fact that some of the PS4 exclusives are great as well.
Via IGN
"It's almost amazing how close they are in capabilities, how common they are," said Carmack, speaking to the hardware capabilities of the Xbox One and PlayStation 4. "I haven't done really rigorous benchmarking [but] they're very close and they're both very good."
Via IGN