Should a web-based UI rely on the browser back button?

The back button is a great "get out of a flow's dead end" option that browsers provide. Should a UI rely on the back button as the only method to allow a user to get to the previous page or should the UI provide an additional, site-specific button to return to the previous screen?

A common scenario that comes to mind with this is an eCommerce site that has a list of products. A user clicks on one of the products to view a details page. Then after viewing the details, they would like to go back to the list to click another product and view its details. Should the UI assume a user will use the browser back button or should the web site provide a link or button that allows users to "Go back to Your Results", leaving the browser back button as an alternative option?