While it would be nice for Apple to get into the gaming scene I don't think they will.
1. Mac Pro uses Xeon Chipset. Show me a Xeon that supports Crossfire or SLI. Go ahead, I'll wait...
Google search and I found an Xeon SLI workstation, to my own surprise, too:
http://www.avadirect.com/product_details_configurator.asp?PRID=4384
Not so much luck on finding a Xeon-Crossfire system
3. PC games aren't dying. They just aren't getting the same level of press like console games. Which is understandable. Console games does rake in more dough. But that hasn't stopped MS from trying to get game development suites cross platform (XNA anyone??).
You may be right, but things have certainly died down since Doom III and Half Life 2 being hailed as next-gen engines. There's also a lot of ports from consoles to PCs, which hasn't worked out well (namely Capcom ports). Not to mention a game like World of WarCraft occupies most people's time now. I won't be surprised if Microsoft or someone else comes back to the PC gaming scene, guns blazing, but there certainly are a few hurdles to get back to PC gaming.
4. IMHO, Apple probably couldn't afford to keep up with the pace of hardware in the PC gaming world. I notice ppl here are super excited about the HD2600XT, why? How come you guys aren't petitioning for the 8800GTX? Shoot the iMac could be using a Go 7900GTX, but it isn't, why? From my understanding it runs in Linux just fine, why not OS X?
Apple has proven it can and can't keep up pace. The nVidia GeForce 3 was a Mac-exclusive for a short time, and we've had our share of Quake 3 and Halo demos at MacWorld. Apple on the other hand cannot keep its graphics card drivers up to date, unless there is more of a push from developers. Blizzard basically forced Apple into getting SMP OpenGL, and when UT2K3 was released, MacSoft forced Apple to update drivers.
I agree the 8800GTX should come our way, but I somehow don't see a mobile chip having staying power in the iMac. The X1600 arguably might be the mobile chipset in the iMac, but the 7300 or 7600 in the iMac might be an indication of things to come. Not to mention, new GPUs mean Apple needs to have new products in the pipeline. The iMac hasn't been updated recently, so no new chip.
This is why hardware upgradability is an important factor for Mac gaming, but it's too expensive since that's requiers Mac Pro. The other is just the sheer lack of developers. Those are the two main factors, as I see it.