In the 5D's case, you're paying 3300 dollars for a 20D/D70 class body.
How so? The 5D has an even more robust magnesium alloy body than
the 20D's, a much larger viewfinder, a 17 frame RAW buffer and 60
frame JPEG buffer, a 2.5" LCD, an RGB histogram, a magnesium alloy
portrait grip, better low light autofocus and focus tracking, etc,
etc. By all accounts, it's been noted that the 5D's body and
mechanical performance is better than the 20D's in just about every
respect. Even if Canon offered NONE of these improvements over the
20D, they could STILL justify the $3300 price for this 13mp FF
camera because it's the LEAST expensive 12+MP and/or FF option on
the market. The 5D is definitely a class above the 20D, and
certainly above the D70. If you think the 5D is equivalent to a
D70-class body, you obviously are selling the 5D far short. Handle
both and you'll see that the D70 and 5D are definitely not the same
"class body".