In 2003, it was granted a DMCA exception to allow it to preserve vintage apps. One site which offers unambiguously legal ROMs that will keep you on the right side of the law is The Internet Archive.
Remember, copyright in the US lasts for 75 years (other countries vary), and issues such as fair use and copying ROMs for which you already own an original cartridge have never been tested in US courts. In the case of ROMs, the ROM emulator is entirely legitimate, but the legality of the ROMs themselves can be called into question. The situation is similar to the legality of IPTV and the difference between the IPTV player app and the IPTV feeds themselves. ROM-based emulated gaming falls into a legal gray area.
