Josh Johnson for J.A. Happ, Dominic Brown, and Kyle Drabek?
They wouldn't even give up two of those three for Roy Halladay, why would they change their mind to get JJ?
Salary and age have a lot to do with it.
I think Johnson is infinitely more valuable than Halladay. He's seven years younger, doesn't have a no-trade clause, and would come at a very reasonable salary over the next four years, if the rumored deal (4 years 38 million) is true. That's a steal for a pitcher who's already very good and likely to get a lot better.