Wow. Really? That a silly reason for an otherwise indefensible UI decision. I really wish the iOS keyboard changed case. Ever since iOS 7, I can't tell whether shift is on or off. Maybe I'm just an idiot, but sometimes I fumble with it a half dozen times before getting it right. It's worse than trying to plug in a USB cable.
The major flailing is the shift key. Right now it's white with a black arrow. That means the sentence started with an initial cap. At any other theme, say mid sentence, it's different again. Mid sentence it's a white arrow on darker gray.
So, in short: about to type cap? Black on White. Mid sentence? white on dark grey. Want to do all caps? Double tap it and get a new version.
I'm not sure how these semantics are different enough from iOS 6 to cause confusion but it does ALL THE TIME.
The same property that makes "BIG TEXT" more difficult to read than "small text" might make each individual character easier to read. I'm not sure that it does, I just don't think your wikipedia page discusses this at all.