Why was there no iWork '07 and iLife '07 announcement at MacWorld Expo?
I suspect the main reason is that the iPhone and (iTV) were made to be the stars of the show.
Steve Jobs stated at The Worldwide Developers Conference in August 2006 that Leopard would include all of Apple's built in apps (I think he meant the same apps that come with a computer, ie iLife).
The full installs of Panther came with iLife 05 ... Tiger omitted the iLife apps ... I imagine we will see the "return of iApps inclusion" with Leopard if not to make it more compelling for upgraders to purchase it and installers to have updated versions of the Apps that are compatible.
Just as 10.3 was A HUGE step from 10.2 - Leopard is A HUGE step from 10.4
My guess is that we may even see Apple do a Microsoft-esque naming scheme and call the iLife release iLife '08 and iWork '08, but release them in 2007.
Here is a link to the 2006 WWDC Keynote:
WWDC 2006 Keynote Featuring Leopard