It has been suggested in a thread on the CSS forum of WebmasterWorld (http://www.webmasterworld.com/css/3500401.htm) that:

One point I discovered the hard way is that any image referenced in the CSS file is automatically loaded even if the image is not used on the page itself. A large background image which might only be used on the index page can therefore slow the load of the landing page.

The linked stylesheet references N images. Only 1 is displayed on this page (below)