In regards to the GPL, the only requirement I can see to report changes to the source is
"5. Conveying Modified Source Versions.
a) The work must carry prominent notices stating that you modified it, and giving a relevant date."
and optional requirement
"7. Additional Terms.
c) Prohibiting misrepresentation of the origin of that material, or requiring that modified versions of such material be marked in reasonable ways as different from the original version;"
Neither of these imposes an obligation to provide detailed accounting of changes or to produce patches.
The only GPL requirement that I can see is to produce the source code that is necessary to build the binary product.
If there is a patch requirement then it is by agreement outside of the GPL. This does not mean that a source distribution requirement can not be satisfied by distributing a patch. It is probably more efficient to do so. But I do not see that as a legal requirement.
If you can find a legal requirement in the GPL to produce patches then please show us. Let us try to avoid creating opportunities for FUD by declaring obligations that aren't there.
I am uncomfortable with implied obligations in contracts. If you think patch reporting is an important enough of a burden to impose on developers then ask the community to add it to the next version of the GPL in an unambiguous manner. I think this is just opening a can of worms.