And you know who buys the top of the line super expensive cards? Pretty much no one.
Then why can't supply satisfy demand? Prices on all the enthusiast-oriented cards have been going up for months, and if you really want a top-end card (5970 for example), it's really hard to find one.
Monitors are getting bigger and cheaper, and a lot of people want to play at (minimally) 1900x1200 at high settings. For newer games that takes expensive cards.