Agree, lots of great points in there. Outside of baseball, the popular sports in America are action-packed, thrill-a-minute type sports. Distance running plays itself out more gradually over time. Kind of like baseball but a big race breaking surge just isn't as exciting to most people as a towering home run. I like the American sports, they are fun to watch because there is a lot of excitement. T&F or distance running events, on the other hand, I don't think I'd be a fan of if I weren't a runner myself. For a non-runner, it's hard to understand everything that is going on. All you see are a bunch of skinny guys running for a long time and one eventually pulling away to win. I'm just not convinced distance running or T&F in general make for good spectator sport.
As for the nationality thing, one thing I've noticed is that it seems like it makes it too easy for people to be uneducated fans. It's too easy to say Kara Goucher, Shalane Flanagan, Ryan Hall, or Dathan Ritzenhein are their favorite runners and they believe that runner is going to win NYCM or Boston or whatever. They don't bother to get to know even the best of the Kenyans, Ethiopians, Japanese, or other runners, even though those are the runners who are actually the ones who should be getting picked as the favorites.
I don't think it's bad to cheer for your countrymate and I'm not sure how much the nation-centric competitions play a role in people doing this (I see the same thing going on, even if the runners aren't entering the competitions based on nationality, at other events) but, when you don't bother to get to know the other runners and won't cheer for them because they are from another country, you're limiting your enjoyment and appreciation of the sport.