"arguing that dynamic linking is Ok, but static linking makes something a derived work smacks of [...] silliness"
There is probably a pretty good argument that both static and dynamic linking create derivative works, either on disk or in memory. The difference is in part to avoid the silliness you describe with regard to copying software in memory, Congress has explicitly exempted the creation of adaptations and copies by end users that are necessary for them to use software on a machine, provided they do not transfer the adaptations to others, of course. See 17 USC 117.
The thing that irritates me the most about the specious idea that a plugin etc is a derivative work merely based on considerations such as utility and compatibility is if that were to become the case, the outcome would be _far_ worse than what little advantage it might gain in some circumstances.
Every Win32 program could require permission from Microsoft to be distributed for example. Or every program that reads files saved in a proprietary format, or supports proprietary network protocol extensions, and so on.