Agree, but I think the GPL examples about communication mechanisms are pretty weird and sometimes absurd. Consider this scenario:

Someone takes a GIMP plug-in licensed under GPL and converts it to a Photoshop plug-in (which is a DLL and shares memory space with Photoshop).

According to GPL, Photoshop would now have to be open-sourced, but the person, who converted the plug-in does not have access to Photoshop source code.

What now? Goes GPL actually forbids the existence of this? What if the converted plug-in with the source code is published? Is that actually illegal? What if they only publish the adapted source code and not the binary? What if a third person compiles it and publishes the binary? Who would be the guilty party?