[sixothree]

The more I think about it, the more I conclude they just cannot afford to support tower or modular designs for the enthusiast market. Not only would they "lose" money from costly upgrades. But it would also become apparent the lack of driver support Macs have; especially as it pertains to video cards.

Maybe the Mac Pro will change the support issue and they will eventually be able to enter this market. But I believe their biggest fear is being compared to Windows or Linux which both have tremendous hardware support.