Update allows Time Machine backups on AirPort Extreme (http://www.macworld.com/article/132613/2008/03/airporttime.html)

Finally Apple delivers (a little late) the ability to use a connected disk on the newer Airport Extremes as a Time Machine backup disk. It's about Time (pardon the pun). :)

That's good because there wasn't any technical reason that the Time Capsule could do it but the Airport Extreme couldn't.

What advantage remains for the Time Capsule ?

1 box rather than 2?

Time Capsule is necessary for anyone who wants the iStack. It's probably faster too.