From the moment the McCain campaign issued its "10 Town Hall" invitation/challenge, it has seemed to me that their real desire is signified at least as much in the "10" as in the "Town Halls." From the beginning, they had to have known that their request was excessive, and that the  Obama campaign would never agree.  Moreover, no matter how much the "Town Hall" format might benefit  McCain, they also have to know that this is a relative benefit; in other words, it's better than a debate, but Obama still seems more likely to gain the immediate benefit from a joint appearance than does McCain.

So why ask for "10 Town Halls" when you know that, even if your opposition were so magnanimous as to grant all your wishes, so many joint appearances are, at best, a gamble for your candidate?  Is this a form of  campaign suicide?  A version of the "Bush strategy," whereby you acknowledge your opponent's intellectual and rhetorical superiority, then lower expectations to such a pitiful threshold that simply remaining upright and speaking makes you seem like a winner?  Or is the McCain camp actually crazy enough to believe that Obama would suffer from the contrasts raised in the course of multiple debates/town halls?
 
I think the "10 Town Hall" challenge is about something else altogether.   The McCain camp wants as many joint appearances as they can get, not because they think the appearances themselves will actually benefit their candidate.   They know that the best they could hope for is a close second (which is why they would prefer the town hall format). The idea here is to try to gain control over Obama's summer travel schedule. They tried the "joint Iraq trip" gambit. Obama didn't take the bait, and it didn't work as a talking point / campaign issue because it was so transparent. They're hoping the "10 Town Hall" challenge will work better because it's easier to frame as a call for "a different kind of campaigning," easier to spin as equally or more advantageous to Obama, and much easier to get the press to move for them (after all, it's not like the networks were clamoring to cover that "joint Iraq trip").

Everyone expects Obama to have an advantage over McCain in a joint appearance. But think about a typical of campaigning for Obama, versus a typical day of campaigning for McCain. Which do you suspect would be more lopsided, in terms of hour-for-hour impact:  a typical campaign day, or a day with a joint appearance?  I'm not just talking about the days with  mega-rallies, or the days with major policy speeches.  On a day with a joint appearance (whether debate or town hall), coverage of the event would dominate.  It wouldn't really matter who did well or who flopped:  the event itself would be the news.  McCain could fall on his face and still essentially come out even with Obama for the cycle, because the joint appearance would capture the coverage.

On a typical campaign day, however, coverage of the two candidates does not break down quite so evenly.  It is more likely that one or the other will "win" a news cycle on a day (week, month, etc.) where no joint appearances are scheduled.  It's not just about who can afford more advertising, or who is ahead in the polls.  One candidate will get more or "better" coverage, and one will say something stupid or give a terrible speech or have to answer for an associate's associate or, perhaps worst of all, simply get overlooked.  Since becoming the Democratic nominee, Obama has been winning most of the news cycles.  Even when competing with Hillary, he made far more effective use of a campaign day than did McCain (after all, we was able to fend off two challengers while McCain gained no ground running unopposed).

Beyond the daily news cycle, each day on the campaign trail translates into votes, money, organization, and other essentials that the candidates will need to see them through to election day.  Joint appearances take a candidate away from the trail not just for the time the debate or town hall takes, but for preparation, travel, scheduling arrangements, etc.  Just as he has won most news cycles, Obama has "won the day" against McCain on the trail:  he covers more ground both in terms of literal geography and in taking his argument to his selected audiences.  On a typical campaign day, he defines the terms of the national debate more advantageously without having to share the stage with McCain.  Obama is not simply a better speaker or a better debater than John McCain; he is, unquestionably, the better campaigner.  This is what the "10 Town Hall" challenge really hopes to address.

I've seen many references to the "losing candidate's strategy" of "debate-as-free-advertising."  I do think the Town Hall challenge works analogously on some level, but I really don't think that the McCain camp wants these joint appearances primarily for the appearance's sake.  I'm sure they would be just as happy if no one actually saw the town halls themselves.  But they do need a way to compete with Obama's dominant campaign.  They don't have the resources, the organization, or the planning to keep up. Obama needn't worry about the costs of personalized campaigning in far-flung locations, whereas McCain has to pick and chose where he will make his stops. Without overstating it, the "age factor" does probably come into play here, as well: I'm sure that McCain doesn't relish the thought of trying to keep up with his admittedly "much younger" opponent's schedule over the next five months.  Perhaps most importantly, however, is Obama's 50 state strategy. As he proved in the primary, Obama is a hands-on campaigner with remarkable abilities to mobilize and motivate on the ground. He has put states into play that haven't been in the "swing" column for generations.

Obviously, I don't want to understate McCain's strength as a "town hall" campaigner.  This is his format, and it does make sense that he would want to try to minimize his rhetoric gap against Obama by debating him in this manner. Regardless of the format, however, McCain can't really expect to accrue much benefit from any joint appearances, as speaking opportunities.  The real advantage lies in the opportunity to influence Obama's campaign schedule with the preparation, travel, and scheduling demands that multiple debates/town halls will create.  The McCain camp has proposed - and will likely continue to fight for - multiple joint appearances in a desperate attempt to divert Obama from personally campaigning in places like Virginia, Colorado, New Mexico, North Carolina, and who knows how many more soon-to-be-blue states?  The "10 Town Hall" challenge hopes to play Obama's rhetorical superiority against his organizational ability.  It's not about engaging issues, and it's really not about "winning" at any particular debate.  By calling for multiple joint appearances, McCain hopes to shift national attention to the debates themselves, and perhaps more importantly, to take Obama off the trail as often as possible.