It is an inefficient way of operating... If I had ten CD players in my house, I wouldn't buy ten copies of Dark Side of The Moon either, nor would I be legally required to, and yet every member of Pink Floyd lives a very comfortable lifestyle from one person, one lisence...
Legally, microsoft are entitled to sell their product under this lisence I'm sure. I choose to disregard their terms, and if and when I am taken to court over the matter, I will stand and be counted for my actions and challenge their practices... As it happens, my spare machines all run Linux anyway at them moment, and there are a couple of old clangers kicking around that run Win 95, so this is not particularly an issue, but if and when I require two or more machines to run windows XP, I will use the same installation disk, becuase that is the most sensible and logical approach...
If one of you can point out an advantage that I have missed to having ten identical windows installation disks in my possession, I will take it on board of course, but until then I am forced to dismiss this "one box, one copy of windows" license as serving no other purpose but to satisfy one company's sheer greed...