Hi Travelrone,
A dry rub is not the same as a cure.
A cure involves the addition of some combination of salt, sugar, nitrates, nitrites and sometimes phosphates and ascorbates to meats, which serves to assist in preservation of the meat and its color. A cure also serves to somewhat enhance the flavor.
A dry rub is a combination of spices that is used to enhance and compliment the flavor of meats, vegetables, etc. Sometimes dry rubs are also used in the marinading and tenderizing processes, but they serve very little purpose in the way of preservation. You wouldn't wash off a dry rub before smoking because you use the rub to add flavor throughout the cooking process. It also serves to create a nice crust, or bark, on the meat which to some is the best part of the meal!
We offer a little blurb on how to use dry rubs at our site:
http://www.carolinesrub.com/using_dry_rubs.aspI hope this helps.