I think the Arduino Due is more of a psychological blow to competitors than anything.
Until a few years ago, the Arduino platform had always had the performance advantage. And now, having a Due (which could mean "Version 2" in Italian) that leap frogs the competition (2-3 x the performance of the DSPic stuff!!!), it silences those people who have criticized the Arduino platform for being lackluster and underwhelming.
You should read the anti-Arduino posts that are spreading across the web, like the ones posted at the end of this article: http://diydrones.com/profiles/blogs/arm-arduino-coming
Like Leon Heller on Avr Freaks, I think the irrational feedback found on those sites is competitor propaganda that's making a serious effort at changing hearts and minds...IMHO
Yes, the performance of the Due is not needed since the Mega can address many of the applications that the Due will handle. However, having the Due with a powerful core will entice power users from defecting to competitor platforms, which is good business for Arduino, since user support from this experienced base has always also been an inherent advantage of the Arduino platform.
I must admit, I'm not much of an Arduino user, but I do occasionally wonder in these forums for insight. And although I sometimes get shocked and awed with the Arduino noobs and their fascination with the LED projects, at least it shows me that they're actually using the platform. Go to the Arduino competitor forums, and there just isn't that much going on.