I don't think that you can equate knowing that you have 'Office XP' vs 'Office 2003' (which is a difference that I maintain is inconsequential in daily use) to

I don't think that you can equate knowing that you have 'Office XP' vs 'Office 2003' (which is a difference that I maintain is inconsequential in daily use) to the difference of seeing your screen move off sideways onto another kind of application. Even if there is no application in another screen, that's still a difference that you at least will experience and wonder about. Sure, web apps are getting closer to native apps and that's a great point (why is switching between web apps that much different than switching between spaces). However, most web pages still tend to look much like a web page and I maintain that people will discover the concept of different applications by associating them with what comes up once they click the dock icons (iCal, Mail, Settings). Another point is that if this distinction is useless to novices (e.g. they don't use the gestures or they don't "get it"), then the more experienced users can pick up on this, and take advantage of this knowledge. Just because it's a fundamental aspect of the gestures does not hurt the novice aspect.