If the vendor requires a license to let you run software on a powerful multi-media (sound, image, input, network) device they sold you, then I can tell you they put restrictions on what would otherwise be a general purpose computer. In my opinion, such crippling should be illegal.
For instance: the iPhone. It would definitely be general purpose if you didn't have to go through the App Store™.
Your microwave oven is different: minimum input, minimum display, one main purpose (heat food). Properly constructed ones can easily be bug-free on the first try, no need for patches. The firmware may even be fused into a strictly read-only chip. Clearly single purpose.
Personally, I'd tentatively set the limit at programmability: if there's any way to reprogram a machine, the user should be able to do it without authorization from the vendor. (We could make exceptions, for instance break control software in cars: such software should probably be tested to death and vetted by regulation. Preventing users from rolling their own may be justified to avoid untimely deaths on the road. Though "preventing" here could mean "legally disallow" rather than "use DRM". Not sure which is best.)
