"Intellectual property" is a meaningless term: GP is specifically referring to rules dictated by copyright laws, which generally allow one to do whatever they please with their "copy" for the most part (as long as they don't hurt the copyright holder's business through a couple of well defined "protections").

Copyright laws were established when it became cheap to "copy" creative works, so creativity would continue to be stimulated by guaranteeing rewards for a set time (idea was not to guarantee getting filthy rich, just to make sure creation happens by keeping the authors fairly compensated).

Digital "sales" are attempts to trick customers into thinking they are buying a copy when they are only getting a license, but this is unrelated to Nintendo killing emulators with an army of lawyers.