I think with the 920 you're mainly paying for PureMotion HD+, super sensitive/responsive touch, and the PureView floating camera. All three are major hardware innovations that you can't get elsewhere.
I hope that HTC and Samsung step it up in their custom apps department. If not, there's a huge discrepancy there too.
The other phones also have their pros over the 920. Both are lighter and thinner so are more pockeatable, 720 means extra row of icons, extra messages in portrait mode, more real state on the browser
HTC has beat audio, a better front facing camera and arguably the better screen.
ATIV has SD card, Bigger screen, Bigger battery, removable battery and the screen has the best blacks.
I would't call Nokia screen a major innovation when the one that saw them side by saw, though the 8X one looked better, the camera is the biggest deal I say.
I do agree on the support part, HTC in particular is abysmal supporting their phones.
I actually quite love the Lumia 900 and 920's design. I'm petite and have small hands, so I normally would opt for a smaller phone, but the 920 is just such a total package that I would get it, regardless of it being big for me.
Camera looks different
Speaker grill is bellow instead of next to the camera
Volume button is placed differently
Sleep button is placed differently
ATIV has a camera button
Aluminum and plastic vs Plastic only.
I understand Nokia (and the media) made fun of the ATIV for being just another boring slab. But there's not reason for lying.
ATIV looks great and is a welcome addition.