What are the terms by which value is measured?
If a website-needing company pays based on how badly it would hurt them to lose that site, it would destroy their margins. If they pay a more reasonable amount, or if they're just a smaller company, they're vulnerable to competitors kicking them offline at a whim.
Land is pretty much the only area where taxing a significant percentage of value makes sense, and even then it's frustrating and awful to do it with a buyout system.
I think in general the business should be bundled with the domain, although I think that probably there should be some oversight preventing completely unrelated domains from being bundled together.