Carmack, once again, misses his mark. He's somtimes right, sometimes wrong. He may have been a genius of coding and may still be quite a respectable engineer, (IMO, he's mostly lost his edge over time, though for me the term "engineer" is not used lightly) but he's still human, and just as fallible as any other genius.
A few here (kinggraves in particular) already pointed it out rather well: smart-phones won't KILL anything: laptops haven't killed the desktop, unlike what it was crowed about since the 90s. Home computers (like the MSX, C64, Amiga, and ST) didn't kill either consoles or PCs, unlike what was claimed in the 80s. Both cases we had the best and the brightest tech minds acting as the doomsayers. In both cases, they were wrong: laptops turned out to fit their own role with only some overlap with PCs, and home computers wound up being squeezed out entirely by more-competitive consoles from below, and cheaper PCs from above.
The stalwarts have always remained, and more or less always will. Sure, you can play a game on a smartphone, but it WON'T compare: people are saying about the "improvement" on them because guess what? We're comparing them to the DS and PSP, a couple of devices that are positively ancient by now. A quick look at previews on either the 3DS or NGP show they EASILY blow away what we see on even an iPhone 4, the HTC Ace, or whatever is the current most-coveted Android phone. (in fact, both look like they can rival the 360 and PS3, barring the cut in resolution, a testament to advancement)
Further, the form-factor, input/output, and cost will ALWAYS form a barrier here: there's no money in making a 3D screen on a phone, nor in putting an analog nub on it. A non-tactile touchscreen with multitouch is the highest they'd bother with, since that's what'd sell a $300-600 smartphone. Similar to 3D screens: while Nintendo (or Sony, if they so chose) have the weight and uniformity in platform to make a 3D-based handheld, smartphones are too fragmented among hundreds of comparable models to ever have any hope there, especially when trade-offs are required.
And lastly, a smartphone has to be nice, tiny, and compact, as, being a phone first, it needs to remain practical as the device you always carry with you, even if it means giving up potential replacements for things you don't always carry with you. That sums it all up: it's a phone first, and just because it can do something, doesn't mean it's always a good idea. Having the best of all worlds is not possible in a device: that's why we still have electronics engineers in this day and age, to develop the best possible options and trade-offs.