As a fellow APSA attendee, let me offer an alternative explanation for Alan's observation that a lot more political scientists attended a clash of civilizations panel rather than one on the future of American Democracy--a diversity of opinion. I'm sure that Kuttner and Mebane had interesting things to say, and there is much to admire in Hacker and Pierson's work--but let's face it, this panel runs the ideological gamut from The Nation to The American Prospect. In contrast, I doubt you'd find a similar consensus about the clash of civilizations among Huntington, Fukuyama, Walt, Barber and Kurth.
It's still possible that the bulk of political scientists attended the latter panel because of their cosmopolitan instinct. I suspect, however, that it's because of the deeper instinct that animates all academics--the lure of a rollicking good intellecual debate.
One other, more mundane explanation--the domestic plenary was held while other panels were going on, while the international one was held during a special time slot.