Those sites have had permission given to do so for that purpose. (And Alla's in the distant past [talking during Kunark era] did take everything offline because of an IP dispute briefly - I think it was just adding copyright info that was missing, but there was a timeframe briefly when they were down from an IP dispute)
Rogean: I'm sure your backend is different, usually that's not referred to as intellectual property though. If he was referencing that as IP that's a odd way to put it.
"A "derivative work" is a work based upon one or more preexisting works, such as a translation, musical arrangement, dramatization, fictionalization, motion picture version, sound recording,
art reproduction, abridgment, condensation, or any other form in which a work may be recast, transformed, or
adapted. A work consisting of editorial revisions, annotations, elaborations, or
other modifications, which, as a whole, represent an original work of authorship, is a "derivative work"."
EQEmulator would fall under this category. It's based off of a concept and heavily modified, without using the direct source material.
It could also fall under "? 108 . Limitations on exclusive rights: Reproduction by libraries and archives" of the DMCA, see: archive.org