The law doesn't do that -- judges interpret contracts "reasonably" not as what they might mean if taken to extremes.
> They have to distribute the complete source with with to rebuild the binaries,
Yes.
> nothing more.
Not quite -- they also need to identify their changes:
GPL v2 $2 (a): You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change
Distributing "base + patches" is arguably one way to do that. "Base + monolithic-patch" might be another. Simply adding a note in the file header is also OK.