I don't think that CSS sprites should be bigger, given that css is improving, I don't know about the sample analysed, but usually the editorial and user-contrib

I don't think that CSS sprites should be bigger, given that css is improving, I don't know about the sample analysed, but usually the editorial and user-contributed content images (as well as ads) take much more bandwidth than style related images, unless the site has exotic design. aside: kranken.io is nice