It isn't just the bronchial tubes.
From national Jewish:
"Bronchiectasis is a disorder of the airways within the lungs. Inflammation and infections cause damage to the airways. This causes a change in the lining of the airways. The airways become distorted and enlarged. Enlargement can be uniform or irregular. Mucus can collect in the airways. The mucus is difficult to clear because of the damage to the normal ways the airways clear the mucus. This can lead to episodes of infection and then, worsening bronchiectasis. "
In the US, 50% of the cases are caused by Bronchiectasis are caused by CF (which creates buildup of mucus anyway which leads to infection anyway which begins the vicious cycle).
Before there was decent treatment for lung diseases it was more common in the US for non-CF reasons (post infection of pneumonia, TB, etc)which also explains why it is more common in countries without good medical treatment now.
National Jewish page <a target=_blank class=ftalternatingbarlinklarge href="http://www.nationaljewish.org/disease-info/diseases/bronchiectasis/index.aspx
">http://www.nationaljewish.org/...asis/index.aspx
</a>
Wikipedia on Bronchiectasis <a target=_blank class=ftalternatingbarlinklarge href="http://en.wikipedia.org/wiki/Bronchiectasis
">http://en.wikipedia.org/wiki/Bronchiectasis
</a>
MedlinePlus <a target=_blank class=ftalternatingbarlinklarge href="http://www.nlm.nih.gov/medlineplus/ency/article/000144.htm">http://www.nlm.nih.gov/medline...ncy/article/000144.htm</a>