@ManipUni:It's not nearly as complicated as it might at first seem, though admittedly it's never going to be as simple as buying a single retail "product". The advantage is that it generally scales  reasonably well for most products (the difficulty usually being around the size where per-server costs start to be better than per-user)

Believe me I've seen far more complex and convoluted licensing schemes than anything Microsoft has ever dreamt up in my time.