It does not help that in the US (or at least in California) you have to drive everywhere. I live in Europe now, but when I lived in the US I barley walked anywhere since it was just too far.

In Europe I do not even own a car anymore. Most things can be done with a bike, by foot, or by public transport. For a few things where I prefer a car, I just use car sharing. So now I am way more active every day.

And thanks to certain trains always be running late, I am running at least once a day as well!

Don't worry, obesity rates are going up in Europe as well, so we'll soon be just like the US!

Well portion sizes are smaller, but most people walk, bike or transit to work. For example this week I haven't done any exercise due to a "sports"-related injury, and yet managed to burn an average of 2571 calories -- and before you think I'm lucky to live near work, my one-way commute is 30 miles. Even just 40 minutes of daily physical activity built into a commute can make a huge difference.

Oh yea, totally. I bicycle to work almost every day (it's ~6 mi one way), but I'm lucky enough to live in a location with decent cycling infrastructure. I think another aspect of why most folks drive here (the US) is because a lot of locations have little or no infrastructure for getting around without a car. In the area where I am originally from (different part of US), you'd get smashed by cars pretty fast because you'd be forced to travel on highways/freeways.

Besides different eating habits, one of the reasons is that there is a huge stigma of being obese in most of Europe. The fact that it is relatively rare makes any such person stand out even more, and makes it harder to justify (since your peers somehow manage to keep their weight in check)