Consider this. I can still buy decent PCI graphics cards. Most of all, graphics card manufacturers want to sell a lot of graphics cards. Only a very small fraction of currently used consumer systems have PCI express. Furthermore, gaming (and perhaps video editing) is the only reason for current home consumers to upgrade - and that's an expensive upgrade when you consider that consoles will cost a couple hundred. As long as AGP is a billion dollar market, there will be AGP cards supporting new graphics processors.
Morever, software developers want to sell a lot of games. Even a year or two from now, an overwhelming percentage of consumer systems will still be running AGP. However, game developers have been known to push the limits more than card manufacturers. The economic reason here is simple, the cost of producing cards scales with the number of cards - not so for copying a piece of code.