I have found that Aussies, Kiwis, Brits, Euros.... mostly a joy to have a game with... Americans, too.
I think that the largest part of the population of WGT is from the US, therefore you are going to find more quitters flying the Stars and Stripes... but it's just the law of averages.
People are going to quit. That is a fact. There is nothing that you, me, WGT or Interpol can do to stop it. You just have to get used to it and not let it ruin your game or your day.
Build a friends list, join an offsite group, join a CC and play with people you know if it bothers you that much.
After all, at the end of the day, this is just a game.
Deal with it like an adult.
Peace