I think its based entirely on the consumer. As long as AGP based motherboards are still popular, companies will have no choice but to produce cards on the AGP bus in order to hit the major sales demographic. The more people migrate to PCIe, the more R&D you will see from the major companies.
-DFI Lanparty NF4 Ultra-D
-AMD 64 3000 Winnie
-eVga 6600GT (PCIe)
-Mushkin Dual Pack PC3200 (512 X2)
-80gb WD SATA HDD
-Creative Live! Series 5.1 surround sound w/subwoofer