DRM crack ?

OK, So I downloaded a movie (.wmv format) and was ready to view it... But it was protected in someway. I discoved a system called DRM (Digital Rights Management) which I'm sure you will already know. It allows you to view the file only when you have a licence.

No problem, I thought. Practically every piece of software available has been cracked in someway, so I was confident I could find a crack that would unprotect my .wmv file.
But... no such luck. I only could find a utility called Freeme, which didn't work for me, since you need the licence file for it.

So my questions:
Why is it so hard to crack DRM? Is this finally a succesful invention from Microsoft? Or will it be cracked sometime and is it just a matter of time?