When including a master stylesheet on a page that has references to images for other pages in your site, are they actually loaded on each page that the CSS is referenced on or are they only loaded only when the page calls for them.

Our IT group is currently saying our sites homepage is coming in at 550,000 bytes according to www.websiteoptimizer.com but that includes large banner files and numerous other background images that are used on different pages other than the homepage.

I didn't think that those referenced files are considered to be part of the page load but I wanted to get your take.