No preconditions for meeting with Ahmadinejad, but he’s got preconditions for doing a town hall with McCain?

Obama today, on McCain’s town hall meeting offer:

The Democratic nominee said his team is in discussions with John McCain’s campaign regarding possible joint town halls and debates. McCain has challenged Obama to 10 town hall meetings.
“What we’ve said is we are happy to do more than the three typical presidential debates in the fall,” Obama said. “If I’m not mistaken we’ve gone back with a counterproposal to them and are in communication with them right now and our hope is is that we will have those negotiations completed soon,” he said.
Ten meetings, however, seems unlikely, Obama said, “given all the campaigning that has, that I have to do since we just finished our primary election.”
The senator guessed the two candidates would meet less than 10 times but more than three and would probably do so in a “mix of formats.”

Let me get this straight: no preconditions for meeting with Iranian President Mahmoud Ahmadinejad, but he’s got preconditions for doing a town hall with McCain?
Second thought — his Senate campaign manager said Obama “thinks he can go into a roomful of skinheads and come out with all their votes” — shouldn’t a town hall with McCain be an infinitely friendlier forum?
Really, what’s the holdup here?