You must remember, we're talking hobbies here. Not bang for the buck.
When you talk about hobbies, everything changes. Take a look at Corvettes. A 1963 is worth more than any Vette made in the 90's. Is it a better car? No, not in any way. Not as well built, not as fuel effecient, parts are impossible to find, etc., etc. Is it more desirable to a collector? Yes!
You can get a real nice 2.8 ghz loaded computer on EBay for $100. Is it as good as the super-dooper $4000 computers you refer to? Of course not. Are those computers $3900 dollars better? I would say no. But to someone who wants to be cutting edge, state of the art, and money is not an issue it's a no brainer to get the loaded new computer.
Dan