See, true professionals know what they like, and can seek it out from Apple's programs or elsewhere. But new users? They don't know what they like, or what they need. They don't know what the difference between an aperture and shutter speed is, or why that's important. They just want to be able to take good pictures and make them look good for Twitter, Facebook, Flickr, cards, you name it. They want it to be easy.
Bingo. I may be an “advanced user” of some aspects of iOS, but when it comes to photography I don't understand half of the terminology involved with prosumer photo apps.
I don't know what kind of precise improvements my photos need. But I know what I want from my photo app – the simple ability to take a picture and have a single copy on all my devices. This is why I could never get into the idea of “processing” my photos: a picture is either good or bad for me, and the basic editing tools in the Photos app for iOS are enough for my needs.
As I wrote before, iCloud Photo Library is shaping up to be exactly what I want from iOS and OS X for photo management and lightweight editing.