Apple knows that a keynote with only one point of view presented can feel lopsided.
By reading favourable quotes from reviews and trotting third-party presenters on stage, Apple gets to say, in effect, "Don't just take our word for it..."
But holy cow, that's a lot of third-party demos in this keynote.
As I alluded to in the last keynote's Memoria section, Apple was blown away with the success of the App Store. The first glimmer of that manifests itself here, when they have an embarrassment of choice when they want to show off some third party apps.
Instead of culling it down to the very best five or six, they march out eleven presenters to demo apps that they've created in the few months since the release of the new SDK. They even drag up an insurance salesman who took a shine to app development and wrote a music playing app in his spare time.
It almost certainly bumped the reveal of Mac OS X Snow Leopard out of the keynote and into the undercard afternoon event, not open to the press and not available to watch by the public. That may have been a happy coincidence anyway, since there were no new user features to announce for Snow Leopard.
After the App Store opened and its success became apparent, Apple still crowed about quantity, but focused on quality in future third party demos. In the iOS # keynote, they demoed two apps, and in the iPhone # keynote, they demoed one game.
The numbers started speaking for themselves, no need for a dozen demos.