I'm just going to copy this entry from Seth Godin in its entirety because I like it so much.

Some industries (like book publishers and analgesic makers) believe that they best serve their audience when the product is available everywhere. It's pretty rare to find a book that's only available in one chain of bookstores, or a pain reliever that's only in one sort of drugstore.

The thing is, scarcity creates value. You can't get a Pepsi at McDonald's. You can't buy Hermes at Target. By limiting choice, you can create value. Exclusivity is often underrated.

Nabbed from Paige.