Originally posted by: MBrown
In what way do they play games worse? Are they choppier? I never understood.
Sometimes the small market doesn't allow optimising for the Altivec unit (the G4/G5 counterpart to SSE). Games are more affected by this than other software (say, Photoshop, which is a well performing Altivec user).
And without Altivec, more or less only CPU speed matters and there Apple felt behind in recent years (one of the reasons they change to Intel).
Except for the Powermac productline it's impossible to change the GPU, which is a drawback for 3D gaming, because Apple's built-in GPUs often are mediocre or low-end (never without dedicated RAM though).
Speaking of 3D gaming, as dclive said, DirectX isn't available on any platform other than Windows. If a game isn't available in OpenGL, porting it to the mac is a PITA. I'm glad Carmack/iD Software think of the Mac/Linux-gamer but many companies decide to support only one platform and that's often DirectX.
Network games between Macs and PCs normally aren't a problem but there's a handfull of games (mostly Microsoft titles like the Age Of * series) aren't because freakin' $35 bil. sales company Microsoft isn't able to port a game network protocol to Mac OS and prefer to write a second one for the Mac version...
Mac games hit the shelves later (few exceptions like Blizzard and iD Soft) and seldom drop in price.
In short, some reasons are home made or based on technical/market reasons but Microsoft as a publisher and OS producer certainly isn't a helping hand either.