I already did contact Apple and they said exactly just that: I woud have to buy a new version. This is just ridiculous in my eyes, as it should be bound to the system or at least it should be transferable from one ID to the other, if the owner changes. What is a server worth without a Server OS? Then they could just sell the mac mini and the OS serparately...
This wasn't the case with lion, where it came with the system! It's a effin' joke and to my personally just another way to make more $$$... I mean it isn't much, but I find this just senseless.