yzedf,
24 hour onsite support may be good, but don't forget, Apple has designed their computers not to need as much support. Regardless, it does not make up the difference in price.
Even when Office XP and Acrobat(not needed anyways) are taken out, there is still about a $700 price difference I believe.
Fire GL is simply the PC version of OpenGL, built into OS X, nothing missing there.
The 2nd hard drive was only added to bring the total storage capacity up to the same amount on both computers (160 GB). Also noticed that the G5 has Serial ATA while the Xeon has only IDE, and two of them already, taking up part of the extra expansion capability.
The extra optical bay is a definent lack, but at least you have a 4x SuperDrive, so most people won't need a 2nd bay. Still doesn't make up for the price difference. Same goes for the hard drives.
Also, you overlooked one thing. The SPEC scores for the G5 are up to 4 times faster than the Xeon, so you're getting a faster, better computer for cheaper, missing only a few minor features.
JW