lack of Vista hardware drivers

We are confronted with massive lack of hardware drivers in Vista.
Over 60% of our office peripheral equipment cannot be used at all when we
upgrade to Vista.

All the HP DeskJet 970 printers cannot print in duplex because HP declared
they do not have Vista drivers for this printers.

All our HP Scan jet C5200 cannot used at all because HP declared they do not
have Vista drivers for this scanner.

All our Dell Nitro 3D monitor adapters (using S3 ViRge/GX IC) do not have
Vista drivers and we cannot set the monitor to display except the lowest
basic VGA resolutions.

So why in the world Microsoft do not allow XP drivers to be used in Vista?

That means we have to roll back all our Vista systems back to XP and new
purchases in XP only.