I think a part of the problem is misunderstanding of how multiple displays work. Win98 has had this feature from its inception, but the solution required multiple cards. The secondary display was just that. No DirectX or special multimedia programs can run on it.
Matrox came in and spoiled folks with DH. DH is *NOT* the same type of multiple display technology as present in natively Win98/2K/ME. The DH is truly a large desktop where the onboard chip controls what is shown on what monitor. That's why you have to run at the same color depth, refresh rate, and resolution. This is usually fine when you have equally sized monitors. Not everyone has equally sized monitors. And I am sure that DH owners aren't too happy with Win2K.
So now, nVidia has TwinView which follows the model of Win98/2K/ME multiple display technology. It allows the OS to have two unique desktop entities as if there were truly two different cards in the system. Again, none of the special software like TV tuners, DirectX, etc. runs on the secondary display. you can run at different refresh rates, resolutions, and color depths. So is NOT a "failure" of TwinView, its a more true representation of the multiple display technology used in Windows and not some hack that tricks Windows.
As someone who has two systems with dual display systems based on two video adapters in each system, I'll gladly take nVidia's approach any day for my Windows and Linux-based computing.
-SUO