No it is not. When you purchase a Windows CD or DVD you purchase the Serial. That is what you pay for. The Media itself can be shared. If not then each CD would be branded with a serial instead of asking for it upon install.
It is not a grey area at all. If it was then M$ themselves wouldnt be able to allow MSDN and TechNet subscribers to download the media as that would be illegal. There is nothing wrong with it. Plus i do know what i am talking about. I am a MVP for Microsoft as well.