I am a bit concerned about some of these changes:
1) Apple does not yet have a statement that Time Machine can use an AirDisk
2) The Airport does not have a statement that the AirDisk can be used with TM
3) TM records into the disk differently when connected directly to a USB drive, it creates a series of folders and stores the backup in a folder with the machine name.
4) TM when connected to a drive via AirDisk, skips the creation of the directory structure and instead it writes the backups at the root level of the drive
5) TM is unable to take into consideration the previous backups that were created when the drive was directly connected to the Mac and does not attempt to convert the old backup to the new format (sparse tree).
Before you answer, I understand things are working, but the big question in my mind is: Is this what Apple intended, for the two methods to produce so completely different results? and Is the fact that is working an accident given that Apple has yet to post the capability?
My backups are very important to me, this makes me nervous.