The new compulsory requirement seems to have been put in place by Apple on Tuesday, when developer Daniel Jalkut noted that apps can now only be submitted to the Mac App Store if the application bundle contains a huge 1024×1024 icon.
This pixel-packed requirement will ensure that all icons are suitable for the new MacBook Pro with Retina display, and suggests that Apple is looking towards launching more Retina Macs in the future.
However, these Retina icons mean that apps will be larger download sizes, and will therefore take up more space on a Mac’s hard drive. The icons will also take up more of the Mac’s memory when rendered, which could cause some older computers to struggle.
Retina-ready apps have slowly but surely been hitting the Mac App Store since the release of the new MacBook Pro with Retina display, but it looks like Apple is trying to push developers in the super high-resolution direction with the new app requirement.