I don't think anyone is claiming that Vista will only run on 5% of machines. What I am claiming is that certain parts of the interface require a DX9 - capable video card. This is different than running DX9. It means certain operations can be done natively in hardware by the graphics card. Apple did something similar with Tiger. Those with Mac minis or ibooks don't see the ripple effect when placing widgets on the dashboard.
This is different than claiming it won't run. It will run fine, but some of the eye candy visual effects will be turned off if the machine does not have hardware capable of rendering them in real time.
Here's what MS has to say about it:
One important thing to keep in mind as youre thinking about the graphics capability of your new system is that while Windows Vista will have a new and graphics-intensive look, it will also be able to automatically and gracefully degrade down to the current graphics look of Microsoft Windows XP.
The new graphics capabilities in Windows Vista will require support for Windows Vista Display Driver Model, if you want to take full advantage of all the new and cool stuff, such as the new AERO Glass look. While more information about specific video cards will come later, some general rules can prepare you for getting the most out of Windows Vista.
If you are building or buying PC today, you probably want to avoid the low end of the current GPU range and make sure you get a GPU that supports DirectX 9 and has at least 64 MB of graphics memory.
Whether you are building or buying a PC today, choose a design that includes a separate PCI Express or AGP graphics card. This way, even if the card you choose ends up not being an optimal choice, you can easily upgrade just the graphics card. And the choice of AGP or PCI Express will ensure that you have sufficient bandwidth to support the enhanced graphics of Windows Vista.
If you choose a system today that has integrated graphics, look at the specific chipsets that are targeted to support Windows Vista Display Driver Model, such as Intels 945G express chipset or ATIs RS400 or RS480 family chipsets. You may also want to consider dual channel UMA solutions and 1 GB of system memory.
When choosing a notebook today for use in Windows Vista, you may run into the trade-off between better graphics or thinner and lighter ultra portables. Exactly which chipsets for mobile PCs will end up fully supported is still open at this point. However, if you are purchasing a mobile PC today, and want to get AERO Glass experience, you will need a discrete card. When buying a notebook today, ask your PC vendor for more concrete information regarding graphics cards that would support Windows Vista Display Driver Model.
Whether you choose desktop or mobile configuration today, not all graphics cards will have in-box drivers in beta 1. Note that, to get the AERO Glass look with beta 1 of Windows Vista today, your system will need discrete cards. However, you should be able to get AERO Glass on systems with advanced integrated graphics choices with the later builds of Windows Vista
Anyone who thinks they'll be seeing the full Aero glass interface on their Dell's integrated video is fooling himself. As far as whether it's important, that's up each individual buyer. On my XP machine at work, all the eye candy is turned off, anyway.