Heh, I grew up in Minnesota (though near Minneapolis opposed to the frigid north) and had to walk to middle school every day, though then I drove to high school (I only lived about a 1/3 of a mile from the middle school, and 3 miles from the high school).

I don't think it is climate though that effects this. The real difference is a combination of how spread out and suburban the US is along with a lack of a strong public transportation. When someone doesn't own a car they are more likely to walk (the article makes an allusion this with the fact that those who take the train to work walk more than those who drive but doesn't go any further). Because the US lacks strong public transport it makes it harder for people to live without cars so they rely on cars more and more.

I've lived the last 6 years in Cleveland and in Washington, DC with another year abroad in London. While I was in London I remember one experience where I wish I had a car (I went to a concert out in the middle of nowhere), but while in Cleveland and DC I have moments probably monthly where I wish I had a car because it takes forever to get somewhere without it.