Someone can (and will) correct me if I'm wrong, but isn't "Plays for Sure" proof that a business doesn't have to go out of business for the company to stop supporting their media?

Even if we knew for sure that Disney would last forever, we don't know that they'll want/be able to support DRMed media they sold a long time ago...

No legal benefit. I suspect, though, that once they charge anything, they need to charge a minimum amount to cover accounting costs, as well as other administration.

Just a theory.