That is completely false, wildlife and nameless npcs totally respawn in all three of those games, just as they will in Skyrim.
I hope so, game wouldn't be any fun if you run out of things to kill now would it?
Oh and some things don't respawn, I'm pretty sure the legendary monsters in NV did not respawn, and I think some of the locations don't respawn legion/NCR, nor do the Behemoths in Fallout 3, or the fire ants if you've killed the queen. And I don't think the enclave outposts that show up respawn. Also I think most of the inside locations don't respawn either, but I'm not sure. And then there are some places that are part of a one time script that won't respawn.
But yes most of the stuff in the outside world will respawn.