I have a co-worker's HP ScanJet 6350 on my desk, connected to the office XP machine that is my "daily drive". I've not had to load any HP drivers—XP supported it from the moment I first plugged it in—and have been testing it with the built-in scanning support tools. It works very nicely.
Here's the Vista angle: the reason my co-worker is letting me use it is because her home system (running Vista) can't support it. When we tried it on a Vista test system at the office, the same thing happens: Vista can't find drivers for this unit, and HP isn't planning on writing any. This is stupid.
It was, and has been my understanding that the USB specification includes (as does SCSI) base drivers for specific classes of hardware. In practical, every day terms, this hardware class support permits the use of drives (solid-state and spindle-based) and interface devices (e.g., keyboard or mouse) without the need to install vendor-specific drivers. Of course, if you install the vendor driver you may find additional functionality, but the idea behind the class drivers is to gain the basic functionality that is expected from that class of hardware.
That said, the situation with the ScanJet implies that there isn't an "image capture" hardware class for USB (even though Windows lumps them together for use with the 'Scanner and Camera Wizard'). Here we have a perfectly good scanner (with document feeder!) that was acquired about 7 years ago for over $300 (in 2000 dollars; don't forget about inflation), and now we're forced into purchasing new hardware to get the same functionality under Vista.
(Note: This scanner is both USB and SCSI capable, but we've only tried it under Vista with the USB connection. The SCSI support in Vista may include scanner class drivers, but I don't have a SCSI-equipped Vista machine to check this out.)
Add to the annoyance: I have an HP ScanJet 6250 at home, which is the older sibling of the 6350. It is connected to my wife's XP machine using SCSI (which is faster than using the 6250's USB v1 port) and it has been functioning nicely for us since 1998. Of course, if the 6300 series isn't supported, it's a safe (and confirmed) bet that the 6200 series isn't.
This is a critical piece of hardware for my wife, so now I can't upgrade her system to Vista (which it would otherwise run well, as it is identical hardware to my Vista desktop test system) until I get a new scanner for her. Grrr!