I reckon designers have been screaming out loud for a 27" iMac and as I use a 27" inch Dell screen (1920x1200) at work I can say that 27" is not too big. 21.5" is a little small but good for having an iMac for the bedroom for example and better than the old rubbish 20" screen.
The MacBook is close to the Pro to tempt you to get a Pro but is still one of Apples best selling laptops. Now with a better screen and battery life.
Not many people get a MacBook Air other than CEOs but it gained Apple publicity so it has a point.
I think designers would have been much happier if the screen had been a 27" 16:10. 16:9 is an TV aspect ratio, 16:10 is for work, and they're obviously plugging the whole high-def movie angle with it. I bet the new Cinema displays won't be 16:9. Should have just gone the whole hog and made a 30" 16:10 model, maybe then we could have had dual hardrives too