Why give up part of the market? Seems like a shame to. New ATi graphics boards and chips will come in two flavors -- PCI-E and AGP, so legacy systems will get some of the benefit of newer technology without users having to completely junk their motherboards (or, more accurately, their entire machines...)

"We learned that the X600 and X300 generation or ATI cards won't remain PCI-E only. As we said, Nvidia and ATI don’t plan to kill their AGP parts and they have to co-exist at least for some time. "

"ATI sees the life of AGP lasting for the next 12 to 18 months so has to offer something to users that want a new graphic card but don’t want PCI-E platforms. "

More here.