But I think many of you are missing my point. Apple will no longer sell a computer that has a powerful gaming card as standard equipment. I don't think most card manufacturers will bother to make a card for people who want to use a Thunderbolt enclosure. That market is just too small.
First, ever since Apple saw fit to putting stuff like Xeon processors and FB-DIMMs inside the Mac Pro, it was patently obvious that Apple saw the Mac Pro not as a machine for enthusiasts and power users the way the old Power Macs were, but as workstations for their "pro" customers. Apple has never seriously marketed their pro desktop line as gaming machines. Whenever it's tried, they either served as fancy benchmarking tools, or as incidental marketing.
Why should Apple cater to the vanishingly small minority who demand that the Mac Pro should compete with gaming rigs from Alienware/Falcon Northwest/etc., or chase after the PC gaming market? Most people in the PC gaming are wedded to Windows and wouldn't switch to a Mac for the world. So who would it benefit? I don't see pro users chasing after the latest and greatest gaming hardware. The notion that Apple needs to cater to the fickle and capricious whims of gamers in order to succeed is a meme which really needs to die out.
I'm not surprised the Steam stats show a heavy emphasis on the Macbooks and their mobile graphics cards; we all know that's the lion's share of Mac sales and I don't debate that. I'd guess that most of them aren't playing very demanding 3D games, either.
...I think not having top-tier graphics cards available will be a slow-acting poison to Mac gaming. I don't know if not having machines that can run their graphics-intensive games at the highest settings will be a deterrent for game companies looking to port to OS X, but it certainly won't help Mac gamers.
Suffice to say, there's more to Mac gaming than "graphics-intensive games". A lot more. And lack of readily available powerful graphics hardware hasnt stopped companies from porting AAA titles before; we got tons of ports back in the 2000s, and that was when Mac gaming was hamstrung by the conversion of x86 to PPC code, not to mention the lacklustre scaling of the G4 and G5.
And it's pretty patronizing to disparage gaming on a MacBook (unless you want to start wading into the elitism surrounding who is/isn't a "true gamer"). The Retina MacBook Pros have pretty good graphics, last I checked.