There is a difference between the Windows license and this - this is a contract. A contract meaning both parties had lawyers in the room (or at least should have) and came to an agreement. With Windows you don't get to change any of the wording, either accept it or not. As such the law and courts place more restrictions on what a license can do - check local laws, but regardless of the wording you may have the right to resell Windows to someone else even if the license says you cannot. However a contract means both parties agreed to this and so the courts are more likely to agree to the wording.

Even in a contract there are limits. You can never have a contract for murder is the obvious example. A contract that is very unfair to one party can be void as well - check with a lawyer for details in your area.