No, for 3 reasons:
1) We have absolutely NO good data for the Fallout series. Fact is, it's popularity was built on a cult following, which means it didn't sell very good.
2) Oblivion launched with far lower numbers. Bethsada shipped around 2 million units of TESIV it's first week. Fallout 3 is over double that.
3) Oblivion was/is the pinnacle of RPG leggery. It sold great at launch on the X360 (250k units) and sold nearly 2 million units in America alone. Fallout 3 will have great legs.
Back from the dead, I'm afraid.