Developer Daniel Jalkut notes that the latest requirements for the Mac App Store include an app icon that's at least 1024x1024 pixels, which is extraordinarily huge. To put that in perspective, each and every submission to the Mac App Store going forward needs to include an icon that's bigger than my MacBook's display (1280x800), and bigger even than a standard resolution iPhone or iPad screen. That's a big icon for sure.
The main reason for an icon this big is the Retina display, currently implemented on the MacBook Pro with Retina display, but presumably coming to even more Mac screens in the future. Icons like this are also used in the Mac App Store in various places, and because Apple's screens are including more and more pixels all the time, bigger icons are required.
The drawback, however, is that a huge icon like this uses up more and more disk space in the app's bundle, not only taking room on the user's hard drive, but also taking up space in the computer's memory when rendered. On cutting edge computers, that's not an issue, but when you're showing dozens or hundreds of icons like this at a time, that memory can add up. Apparently that's a trade-off Apple's happy to make.
[via Shawn Blanc]