Actually, David, Apple and Microsoft offer special 'family packs' that allow private buyers to install MacOS and Windows on multiple machines (5 and 3, I believe) as long as they are part of the same household.
With regard to MorphOS, it is more likely that development is stopped and everybody gets a free key than this being implemented, however. The current licensing scheme was chosen because of its low administrative overhead. 'One price for all' is really as simple as it gets.
