another factor might be that while for a you almost needed a new video card for every game as the games minium system specs went up with almost very release.. that's not so much the case now.. take a look at this sampling of game video requirements:
Ruse: 128 MB DirectX® 9.0c-compliant video card ATI® Radeon X1000/GeForce® 6 Series
fallout3: Direct X 9.0c compliant videocard with 256MB RAM NVIDIA 6800 or better / ATI X850
starcraft2:Video Card 128 MB NVidia GeForce 6600 GT/ATI Radeon 9800 PRO video card
disciples3: nVidia GeForce 6600 / ATI Radeon 9600
bioshock2:NVIDIA 7800GT 256MB graphics card or better, ATI Radeon X1900 256MB graphics
Supreme Commander2:128 MB VRAM DX9 compliant with Pixel Shader 2.0 w/ instancing support
simply put, we are not upgrading video cards as often add that with economy and the fact that software advance are allowing for some pretty cool things with current tech and I can see why for some companies it might make sense to change what they do or fall by the wayside when demand is less...