Different in multiple ways, some rather obvious like the hip belt! Also 100g in weight, toughness of materials, where the zip openings are etc.
The other thing is that the number of little touches they've put on the grams is astonishing.
Lets see if I can remember them all:
those one hand openable/closeable bottle pockets, expanding hip belt pockets, external bladder pocket with a hanger, internal mesh security pocket, tiny little attachment pockets for those add on pockets they're doing and probably more....
I'd say that they all explain the price, although its obviously a personal decision if they justify it!
Not entirely certain in general, I got a gram 25 as it was the first small pack I'd found genuinely long enough to work well for me.