Mac Pro: 2.66 GHz Quad Core, 6GB 1066 MHz RAM, ATI Radeon HD 4870, 1TB 7200 RPM, etc. ~$3000.
PC: 3.2 GHz Six-Core O/ced to 4.2 GHz ($900), 12GB 1600 MHz RAM ($400), Nvidia Geforce GTX 470 / ATI Radeon HD 5870 ($350/$400), 2TB x 2 in RAID0 ($240) for offline storage, 128GB SSD x 2 in RAID1 ($500), X-Fi Fatality sound card ($200), a superb enclosure, high end motherboard and cooling system plus all the necessary accessories ($500), opportunities for endless tweaking, etc. ~$3000.
Besides, PC has NEVER failed me.
Your comparing Apples to Oranges.
A) Your comparing a prebuilt computer to a home built one. This means you dont have a warranty or easy tech support. This means you may have compatibility issues. This means that you have to invest more time ($$$) into building and maintaining your rig. This is not factored into the cost. Go spec out a comparable machine from Dell or HP and see how close they are to Apples price for WORKSTATION GRADE computers.
B) Your pricing for the PC is on the cheap side. $500 for a case/powersupply, motherboard and cooling and accessories is low. A decent mobo is around $300, cases with power supplied are $250+... And you didn't include the cost of Windows or the other software that ships with a Mac
C) comparing an overclocked computer to a stock workstation in terms of speed is fine, but how do they compare in terms of reliability. Fast render times are great, but not if it crashes mid-render and you need to render the project again.
"A PC has NEVER failed me" That is a ridiculous statement, and not something that I would count on for a production computer.
Mac vs PC is something that some people can't look at objectively and include all the relivant facts. You need to look at the total cost of ownership not just that cheapest system you can buy. This includes support, cost of downtime, software, the time to spec and build/install a machine.
I am not saying that a mac will be better or a pc is worse, but simply that people need to be fully aware of what their choices are and that its not simple to say this is better because its less money NOW.