Circumventing an effective copyright measure (use) is a violation of section 1201, as is trafficking in circumvention tools (distribution). The major difference is that the act of circumventing itself may be protected by one of the exemptions approved by the Librarian of Congress every three years; there are no exemptions of any kind for the act of trafficking (which means that distribution of bnetd and PVPGN is illegal in all cases).
Near as I can tell, circumventing the access restrictions to enable netplay on a video game that is no longer distributed is not a DMCA exemption. (Circumventing DRM for a game whose DRM servers have been shut down is an exemption for local play only.)
Protocol reversal is not a DMCA violation. Otherwise MS would be in big trouble for when they reverse engineered the AOL protocol for the MSN Messenger.
You can't copyright a protocol.
So long as these systems aren't enabling pirating these classic games they are free and clear.
One of the things about battle.net though was that pirated StarCraft copies couldn't connect to it. Battle.net thus served as an "effective" copyright protection device -- circumvention of which is illegal under the DMCA. This has been tested in court, and the court found in favor of Blizzard. So yes, a judge has ruled that reversing the Battle.net protocol is a DMCA violation. That's why the bnetd.org domain was awarded to Blizzard (though a US court could not prevent the distribution of bnetd outside the USA).
