Well yes, they ought to be preserved. Which ones? All of them. There's no reason not to. It's not as if preserving data is the same as preserving physical art like paintings or statues. You don't have to allocate physical space (well, you do but not in the same sense), pay for protection(thick walls, guards), or take measures to protect data from the air itself.
How? Emulators in the case of consoles, and compatibility layers and DRM cracks for PC games. I don't think publishers or console manufacturers will play a major part in the process because it doesn't make sense for them economically.