|MadSci Network: Microbiology|
This is a very good question.
You are right in that many types of rinds are simply formed when the cheese on the edge of a wheel dries out because of exposure to the air.
Some types of cheeses ( Gouda comes to mind) are given a wax coating to seal in moisture and prevent the formation of a hard rind.
In Brie cheese the rind is actually formed when the surface of the cheese is fermented by a mold ( Penicillium... the same species that makes the antibiotic penicillin)! Camembert is vert similar to Brie, and also has a mold ripened exterior. Limburger is an example of a cheese where bacteria (not mold) are used to ripen the surface of the cheese.
Try the links in the MadSci Library for more information on Microbiology.