You are probably right about the shift in emphasis.
This prosecutor wants some meat for the cost of putting on the show, and if he comes out with nothing, there will be a lot of crap.
So I think it's perjury he will look for, even though it won't hold up at trial.
A perjury charge is actually worse politically then the "plame name" charge. the sheeple understand the word "perjury". they don't understand releasing the name of someone - its no big deal to the average american to release the name of someone who is on the cover of vanity fair.