Unconventional exercise

No, not sure at all. Reduced function of the nose is part of the reason people get more colds in the winter at least (I read lots, but remeber poorly).

I read an newspaper article last year about a paper that suggested that the increase prevalence of viruses in the winter was more due to people spending more time inside together mixing with more people in warm damp environments where the virus could transfer between hosts easier resulting in increased risks.. Again this was however a newspaper article about a scientific paper and newspapers don't always interpret scientific papers correctly.

Somewhat connected....
I have recently discovered that my one year old has astma. I asked the doctor if we should keep him indoors during colder days (say minus 5 - 15). The doctor did'nt see any reason to unless he was already ill. So the extreme cold is possibly less harmful to our lungs then we imagine.

Quite possibly. Mammals exist in very cold environments. What repertory physiological adaptations they have to cope with the cold I don't know, perhaps an elongated nasal passage?

I did'nt like the quote myself. There are simply too many variables. But I am frequently told that this is true (by very unqualified people though). I do get the cough mentioned in the article, and have dismised it as a side effect of the cold dry air, and not a sign of illness (It only lasts less than an hour).

I always hypothesised that that the cold weather cough is more an initial spasm to muscles due to the cold air which passes after a while as your blood flow adjusts.