Poulscath: Not quite the same. Fallout was a limited time offer. C&C is more like how Bethesda released Daggerfall and Arena.
SimonG: That doesn't matter. They didn't forfeit their property to the game, they just offered the "gaming license" free. For how long you do it isn't an issue. Bethesda, EA or everybody who owns games that are given away for free can simply say "fsck you, from now I'll make you pay for them". But that doesn't render the copies you already have illegal, of course
That's generally how that works. Ultima IV is free, but only if you download from somebody authorized to provide the downloads. Anybody else providing it and it's technically pirating the game.
What would make it different is if EA placed the game into the Public Domain, any copies that they placed into the public domain would always be in the public domain.
The whole BS of taking PD works and putting them back under protection is something that just risks losing works to non-ownership.