Who knows why it took so long, but the latest AirPort Extreme firmware update (7.3.1, out today) finally brings Time Machine compatibility to AirDisk. In typical Apple fashion, there's no mention of it on the release notes, but the crew over at TUAW says it's working, and commenters are confirming. We're still holding out for Time Machine to work with any NAS we want, but for now, it looks like all you Airport Extreme owners who felt like you were getting played by the release of Time Capsule are finally in the game -- get those USB drives ready for some hot backup nights.