what keeps some nosy haxx0r from looking in the MBR (or some blocks later) if he wants to find out about the copy protection? if they store data like this unprotected (e.g. crypting them) then this is just security-by-obscurity (which is no security at all).
Copy protection IS security by obscurity from a cryptography point of view ;-)
http://en.wikipedia.org/wiki/Kerckhoffs%27_principle
The thing is that the user HAS to be able to decrypt the movie / game / whatever and use it, so in some form he HAS to have the keys. The only thing that can be hidden is the algorithm and the location of the keys(sort of part of the algorithm). This can't work from a mathematical point of view.
What makes copy protection problematic to circumvent is not the math or the technical stuff, it is the laws protecting it :-(