Consider the video games of the 1980s. Arcade games, Nintendo games, Sega games... The list goes on. Both Nintendo and Sega have long ceased production of their original consoles, the NES and Master System. I highly doubt many of the arcade games of the 80s are still active. None of these companies are making much, if any, money off of these systems. Neither are the publishers of games from the NES and Master System.
Aside from the fact that these games are no longer produced and available for sale new, you could also think about how the technology used in the games has improved and there is now a higher standard to be set by games. When you look at the original Super Mario Brothers game and then look at something more recent like Luigi's Mansion on the GameCube, what are more gamers most likely to play? Certainly younger gamers, those who did not grow up knowing the old side-scrolling games would be more interested in what is available today. Maybe some of the older gamers, too. Myself, I still enjoy the old games and play them from time to time. Some of the games are lost, however, because you can't find them anywhere to buy, only on the Internet where they can be downloaded - illegally at this point.
Currently the copyright limitations for these games would be something along the lines of at least 70 years, thanks to the Copyright Extension Act of 1998. As far as I know, these video games fall under this law, meaning the soonest that the games of the NES and Master System could be freely available is somewhere around 2055.
Are any of these companies still making money off of the original games? Not likely. Certain game franchises like Nintendo's Mario and Luigi, as well as Sega's Sonic the Hedgehog exist to this day, but I don't think that means that they still receive income from those first games.
I wholly believe that game publishers are entitled to keep their games under copyright. However, does it really make sense for those companies to hold on to them for over 70 years? Games are a bit different from books, music, movies in that interest in games holds for considerably less time.
Releasing the games to the public could present many benefits. It would be good PR for the developers, for one. It would also help these games last for a very long time - the Internet is currently the best system for archiving our history and culture (currently it seems that thanks to P2P applications music and movies would last for a very long time). Finally, it could mostly serve as a way of interesting people in current games, much the same way that some people use MP3s to "try before you buy". Personally, I would also just like to have these games again.
I believe that the game publishers (for both console and computer games) should release the games into the public domain, available as ROMs, for example, after a given period of time. Whether this is by choice or by law, I don't think it matters. Releasing the old games is not going to cause financial harm to these companies, but making them publicly available has its benefits. Keeping them under corporate control for so long just doesn't make much sense.