@ Omegon3: I was disappointed a while back to find that the free buildings only go to the civ that actually builds the free-building granting wonder (in my case it was the Catacomb Libralus). I believe they still get this bonus after losing the wonder too.
@tipwong: Ah, you mean expansions. If FfH moves to the expansion then you would need to buy the expansion, otherwise not. Kael chose not to move FfH to the Warlords Expansion, but then decided that moving to BtS was a good idea (he actually new about BtS back when Warlords was first releases, since he was asked to work on a scenario for it. He knew it would add far more to the game than the first expansion did, and didn't see much point in making everyone buy 2 expansion sets). He actually started over on the BtS version, so presumably the same would happen if there were another patch. Of course, I don't think there will be another. Version .23c is the last version for vanilla Civ IV, and all later versions (including the current .30, all future Shadow versions, and Ice) are for BtS.