If they had to list everything it does NOT work with, well you could not lift the box.
THis is a rather different situation, though, Chris. The point here is that iPods always have worked with firewire in the past. Mac users with a long history of iPod use particularly had a pretty reasonable expectation that the iPod would still be firewire compatible. Heck, for the first part of their life they would ONLY work with firewire.
It seems fair enough to me, under these circumstances, for people to expect that a change as substantial as this would be mentioned on the packaging. It is really is a very different situation from the other "cautions" you suggest. I would also expect sales staff to be well enough trained to make the matter clear to potential purchasers. I knew the situation already, but I certainly wasn't asked anything at all about the suitability of my computers when I purchased three gen 5 iPods for people as Christmas presents. It would have been better consumer oriented sales practice if I had been. Caveat emptor is all very well, but people have come to expect a bit better than this from Apple.
Under the circumstances, whatever the merits of the actual decision to move to USB2 only (and I can see pluses and minuses here), I can readily understand quite a few longstanding Apple customers being upset about the matter. These sorts of changes always generate some 'heat" (as quite a few of us with an inventory of SCSI peripherals when it gave way to firewire will remember!). Trying to tell them that its fine that they can not use the new iPod effectively with their 2 year old computer is never going to be a convincing line! I reckon all we can really offer people here over this change is some well deserved sympathy.
Cheers
Rod