To be fair it's a new style language. It's going to take time for people to normalize on designs. Eventually I think that there will be a more homogeneous experience, but right now everyone is trying to feel it out and explore. Design follows trends, but right now there aren't any trends to follow in ios7.
Previously, wasn't it just follow Apple's style guide or go home? If so, what's happened in iOS 7? Are Apple just being far more lax in enforcing a style guide or is the style guide out of the window now?
Nope, that wasn't really the case before. There were plenty of apps that deviated from Apple's styles, it's just that their UI tools made it easy to design your own app with your own interface. I think we'll see a lot of apps that look like stock iOS apps once the app makers that have been holding off/don't have a UI Team realize they need to update their apps to match the modern visual style.
