Supply and Demand
Yea, no one wants AGP anymore.
:? This doesn't make sense. If nobody wanted AGP cards anymore, their prices would be lower based on economics. It is more likely that fewer AGP cards are being built and the manufacturers want everyone to upgrade to a PCIe card. When there is an interface change like this, everyone eventually has to upgrade, which is good for business.
As far as the bridge chip is concerned, I can't see any way that one little chip is making the entire cost difference on some models. I don't think this plays a very large part in the pricing.