Retina MacBook Pro displays iOS-like low battery indicator

If your Retina MacBook Pro’s battery is too low to start up, its display will show you an iOS-style, color icon like the one pictured. Thanks to Dustin Curtis for use of the photo.

Double-check: I don’t have a non-Retina Mac in the house to test this, but could this be a Mountain Lion update? Or is it custom firmware in the rMBP?