Why not make it a single activation licence like Apple do with thier OS's and let people play with different ram, graphics cards and CPU's. After all they all need replacing in occassion.
I don't really see your point - it is a single licence and MS allow you to change components - they just ask that if there is a significant change (or changes) that you reactive the product

The only time this isn't ok is a motherboard change with OEM (although recently the whole issue of OEM licensing has been called into doubt).