You can write whatever you want in a license. That doesn't mean that it's legal or can stand up to court challeneges. The fact that you haven't seen the normally litigious RIAA go after anyone is because precisly this.
When you buy a copy of something copyrighted, it's yours to do as you want. I know the courts have continuually upheld this in the past with physical goods. The jury is out on digital goods. I'm sure the RIAA would love nothing than to exclude digital goods from these existing laws but they're probably hesitant at this point of setting a precident in the courts which would destroy their rights to limit and control digital goods in the foreseeable future.
There are a lot of nuanaced characteristics in copyright laws. I know that one sticking point that the copyright holders have made in the past has been that digital goods are not the same as physical goods such as books, DVDs, or Bluray discs in that it does not degrade. Hence, existing copyright laws and courst case in favor of allowing anyone who puchased a physical good to do what they want with it doesn't apply. Like I said, I don't think there's been a definative answer as of yet. Cases are still being decided.
As far as not paying for a digital copy with your existing DVD/Blu-ray, you guys couldn't be further from the truth. The fact of the matter is that you ARE paying extra for the extras. If you buy just the Blu-ray, it's one price. If you want a DVD and a digital copy to go along with that it's a higher price. If you havn't noticed the different tierd pricing structure you must be blind. So, you are in fact paying for your digital copy. The studios are just smart to try to hide the fact by bundling it.
It seems that many of you havne't noticed which was exactly their intent.