LH, the viewpoint on that webpage tolls like a funeral bell. It is lucid, historically accurate, well-presented, and worst of all ... it really does fit in with a lifetime of personal experience with smoking.
As a light-to-moderate smoker, I've often wondered if it's that extra coating of mucous - that little "smoker's cough" which is really more of a throat-clearing than a cough - which protects me from the atmospheric irritants and that cause asthma and allergies in the non-smoking members of my family and so many others I know.
I spend my life teaching private music lessons to kids with colds and various stages of the flu. How is it that I, a supposedly sickly and oh-so-vulnerable-to-every-disease smoker, never "catch" their bugs unless I'm also very over-tired or otherwise stressed? Could it be that same protective coating in my throat and lungs?