The important point is that it's orthogonal to search.

You can make SEO-penalization as complicated as you want without affecting search. The only thing search should be able to deal with is a SEO-penalty which is just a number.

Is your point that SEO-penalization is just a sorting implementation concern? I think Google does far more than that - perhaps removing/banning sites or categories of content that are deemed to be gaming their system.

No, I was replying to what derefr said.

And removing/banning sites can be done by setting the SEO-penalty to infinity.

I'm not trivializing anything. All I'm saying is that the concerns can be separated.