STENDEC said:

Also, reading the response from Lucasfilm that the LoC could ONLY show the Special Edition, even for just a private screening, is absolutely disgusting. If it were up to me, I would've just exercised the right to show it anyway. If Lucasfilm don't want to oblige the LoC in any way, why should the LoC oblige Lucasfilm?

Presumably because LucasFilm has far deeper pockets to survive a lengthy legal battle, than does the National Film Register.

This is not a money issue. Both sides have pockets that can reach till deaths. The LoC is in no position to challenge an active copyright. Their mandate is protect until expiration. But your issue of the showing of Star Wars is a NFR issue. The Nation Film Registry is not a requirement. It was set up to help preserve films which the public deemed worthy. No one is required to submit new prints to it. (as i'm aware of it) It really is a ceremonial organization. It means well, has no teeth and only time will tell if it accomplishes it's goal.

It's all PR as LexX alludes to. It's bad press for both sides if the list ever gets out of who did not submit NFR copies when asked. People could read it as the creator/copyright owner doesn't agree with the group and contrarily the NFR is failing to meet it's challenge.