Does bronchitis affect the healthy?

Yes... Acute bronchitis is due to an infection in the airways and otherwise healthy people can get this. Chronic bronchitis is a form of COPD that is typically caused by smoking. Smokers who are otherwise healthy can develop chronic bronchitis.
Yes. Bronchitis can affect all, whether healthy or not. Bronchitis is an inflammatory condition of the bronchial tree. This inflammation can have many causes, including infections, allergies, irritants, etc. Healthy individuals can be affected by all of these causes. However, when healthy you are less likely to pick up infections due to a presumed normal immune system.
Yes. Bronchitis can affect anyone, but is more likely to be seen in those who are debilitated or have preexisting lung disease.