They always release DLC and Expansions, but 2008 was the first time they have ever released a Fallout game.
I know?
I said they will probably make some additions to Skyrim before they release the NEXT fallout title.
As it is usually the case with Bethesda titles, in that they get additions before the next release.
There was two expansions and some minor DLC for Morrowind and one and a half expansions for Oblivion (KoTN kinda almost counts as a little expansion I guess...)