Not quite. The FO3 game engine was a progression on the Oblivion game engine, and the workflow was already sorted out from building Oblivion.
Not sure how much impact that would have on your example, though...
In fact, Bethesda's step from FO3 to Skyrim was the big one in terms of engine, since they drastically reworked the scripting engine, started using a completely new animation system for actors, and introduced a major new gameplay element (dragons, which were both flying and walking, and had far more complex air-to ground combat than any previous creature in a Bethesda game).
[edit]
Heh, ninja'd by REL_dovahkin