Companies that avoid GPL also avoid licenses that forbids DRM and guaranties access to source code.
But to reiterate the four freedoms:
Freedom 0: The freedom to run the program for any purpose. With DRM this is impossible. The DRM business model to prevent generic parts rely on users not having freedom 0.
Freedom 1: The freedom to study how the program works. Without this researchers can't do inspection of medical software or voting machines.
Freedom 3: The freedom to improve the program. Without this a person can't improve their tractor that they bought, even if they are by law the private property owner of the device.
That leaves:
Freedom 2: The freedom to redistribute and make copies so you can help your neighbor.
So for the cases above, three out of four software freedoms is required.
But to reiterate the four freedoms:
Freedom 0: The freedom to run the program for any purpose. With DRM this is impossible. The DRM business model to prevent generic parts rely on users not having freedom 0.
Freedom 1: The freedom to study how the program works. Without this researchers can't do inspection of medical software or voting machines.
Freedom 3: The freedom to improve the program. Without this a person can't improve their tractor that they bought, even if they are by law the private property owner of the device.
That leaves:
Freedom 2: The freedom to redistribute and make copies so you can help your neighbor.
So for the cases above, three out of four software freedoms is required.