I suspect (I'm a non-obese non-smoker) that far more obese non-smokers get winded by walking such a distance than non-obese smokers, at least until they're fairly old. Also, in walkable cities, I see quite a few smokers but much fewer obese people. If we're talking about hiking hills, it balances out a bit more, although I think the obese would still be at a disadvantage. Losing some of your lung capacity doesn't matter too much until you do intense exercise, but obese people always have to expend extra effort to carry their weight around.