[gerrit]

Except that designers might want to include 4x-sized bitmap assets to have their sites appear sharp on those retina displays. If that isn't done carefully, users with smaller displays might have to download those, wasting their bandwidth.

[webjprgm]

Hmm, yes, especially if the designers are working on such a large resolution screen.

Would the solution be a media query in the CSS? Would there be data in the HTTP user agent string to serve up a different CSS/HTML/image resource?

[gerrit]

Apple introduced the -webkit-min-device-pixel-ratio: 2 media query parameter with the iPhone 4. But for HTML images that doesn't help