The solution to this *people* problem is simply : policies + training.
I don't completely disagree with you, but I'd extend it to say "Policies + training + audit".
the microsoft solution, amongst others, provides a way to do this audit. it's not perfect, there are ways around the protection, but those ways rely on the person actively trying to get around the system. they know they are doing something wrong. these document DRM systems provide a framework so that the users can easily see what what they are supposed to be able to do and it prevents them from doing what they're not supposed to be able to do.
it also logs all document requests which can be viewed later. in the OP's case, he stated that requests to open a document from overseas might be suspicious. he can audit the logs from a DRM server to see where requests to get keys come from.
dave