There has been some speculation that the entire Wilson/Plame story is a diversion from more sinister actions:
The African Connection: Rep. Jefferson and Joe Wilson
That does not specifically explain Fiztgerald's actions, but it does help to understand the timing of all this distancing from Wilson that seems to be going on. The court decision about the Jefferson documents seized from his office was due (according to the above link) on the very day that the Armitage connection was more or less confirmed in the Isikoff/Corn story. That the Jefferson decision has not yet been announced is interesting . . .
I'm surprised Jefferson hasn't claimed the money came from his share of helping a Nigerian bureaucrat take his money out of Nigeria. I get those offers all the time.