timppu: If the Wikipedia-definitions are to believed, disc-based copy protection systems (like the good old CSS for DVD movies) are also DRM.
Every time a person uses wikipedia as a source a cat dies.
Seriously though, disc-checks do not manage your access to the data after the sale. As long as you possess the disc you have access. DRM means the company can control the product after the sale. Hence copy protection versus DRM, two different things. A DVD movie has DRM on it according to your definition.
And I have to agree with some people here, disc checks have given me more problems than DRM has. Splinter Cell Chaos Theory, Crysis and FEAR were particularly bad ones in my experience. Never had a problem with Risen, to be fair.
The problem with DRM for me has NEVER been ease of use though, DRM has never caused me a problem. The issue with DRM for me as always been longevity, making sure I can use the game when the company is gone or ends support.