There will always be a difference between people who need more than a stock computer, Professionals that need a workstation, and people who just want the best of the best.

I personally fall under the professional workstation category and thats why I shelled out almost $10,000 for my set up. I needed something that will work 24/7 and could run circles around any other computer that I have used. I can justify the cost because the computer lets me get more work done in less time so that means that I make more money. But for someone who doesn't make money off of their computer spending $10,000 would be ludicrous.

Gamers and the people who just want the best of the best can get the same performance as I do but their system might be less reliable. The major difference here would be Xeon vs i7. (price wise as well)

Rich is right. Most pre-built PC's are crap, and I would be wary of Pre-built customs. If you know what you are doing/where to look you can build a monster of a computer for a fraction of the price that a Pre-built would.