Archive.org apparently has a DMCA exception. Does that mean downloading ROMS/ADFs/ISOs from their TOSEC section legal?
The DMCA exception they have only covers circumventing copy protection on old software that they legally own. It doesn't give them permission to distribute the files.
When they receive DMCA take downs, they hide the files from the public.
Downloading from archive.org has the same legal status as downloading from anywhere else.