Also the Mac Pro is not a regular desktop. It is Server Hardware.
1. Server class 1KW powersupply.
2. Server class ECC ram
3. 2x Server class Xeon processors (The CPus themselves cost 1K a pop)
Just in processors you have 2 grand right there. Go google prices on Xeon Cpus.
Thats why those mac pros look like one big solid box of thick aluminum alloy. Just the door weighs more than the entire case of one of those dells. The whole thing is toolless.
The PC board is also thicker and more robust than the PC boards on regular dell desktops etc.. (more layers)
I could run a shit load of data all day long and thing does not break a sweat. Uptimes of weeks and weeks no hiccups. (only time it is disturbed is when downloading an OS patch ie: 10.6.2)
With Unix I run different kinds of applications for analysis and modeling. Stuff ported from Solaris and Unicos (Cray Operating system) Nice to be able to get source from a Cray and compile it on the box and run it.
PC and windows 7 is a toy, Real men run Unix workstations
Remember heavy duty Powersupplies with large caps,coils etc.. prevent glitches that cause crashes,lockups etc..
ECC ram also prevents memory corruption which could mess up the data in ram causing incorrect results over time,crashes,lockups etc.
Xeon Cpus have ECC ram in cache as well.