Its not a secret Apple uses the videocard handicap to get people to buy new Macs. They have done it for decades.
Please forgive my iMac-owning ignorance, but exactly what is so unbearably awful and terrible about the video card that came with your Mac Pro? Does it not display colour? Are you limited to 320 x 200 pixels? Is it completely incapable of playing back a Quicktime video? Or is it just that now, a year later, there's something new and better on the market? For exactly how many years did Apple guarantee your purchase would remain state-of-the-art, anyway?
If you bought a 2007 Civic, would you demand that Honda make the 2008, 2009, and 2010 engines, radios, and wiring harnesses drop right into it? Of course not -- demanding that everything remain backwards-compatible would handicap new technology. So maybe it's not Apple that's handicapping their video cards -- maybe it's the owners of yesterday's technology who collectively freak-out and demand backwards compatibility the moment something better comes along.