iOS7 has followed a trend that has been popular across many platforms.
The important point I want to focus on is that iOS7 looks dramatically different from all the versions of iOS that have gone before. Head over to http://www.apple.com/ios/ios7/ if you've not had a good look yet.
The difference matters because many apps, brands and companies have taken all their branding cues from earlier versions of iOS.
If you're a Windows Phone or Android user (or developer) you'll have no doubt noticed the number of apps that were first created on iPhone and then ported to other platforms but kept the original, iOS appropriate visuals and styling.
I predominantly work on creating Windows Phone apps that already exist on other platforms. (It's typically only apps that are successful on other platforms that can afford to pay to get their app ported.) One thing I hear a lot as part of my work is that the company behind the app sees the way the app looks on iOS as part of their branding. They don't necessarily says this directly but that's the underlying idea when they say that they want it to look like it does on iOS.
Some time ago, when they created their app they, rightly, wanted it to look like it belonged on the device and OS it was running on. No doubt, for most companies this was a new experience and probably not straight forward as they adjusted to how their traditional branding and visual identity was represented on this new small screen.
After such a complex and time consuming process I suspect one of two things happened.
1. They got so used to seeing their iOS app they lost sight of what really composed their original brand identity and what they regularly saw took over.
2. They didn't want to go through the hassle of adjusting their visuals to each new platform. They've done that already. After all, aren't all mobile platforms the same.
This is where iOS7 raises an interesting scenario. If there are lots of apps/companies/brands who take their app design influence from iOS, what are they going to do with this update?
If they leave everything looking like it did on iOS6, then when run on an iOS7 device it's likely going to stick out like a sore thumb.
Similarly, if they update their app(s) to solely adopt the new iOS7 styling then it will stick out, for the wrong reasons, when run on devices still running iOS6.
As not all devices will (or can) be updated to run iOS7 the only option for companies wanting to continue to support all iOS users, regardless of which version of the OS they have, the only option is to have an app that adopts its display based on the OS it's running on or to have different versions of the app(s) for each platform.
The important point here isn't that they have to deal with further fragmentation; it's that people are going to be forced to think about making their visuals and styling appropriate to the platform they're running on as part of wanting to make a great user experience.
My hope is that, once companies are forced to look at providing a platform specific visual experiences across the different versions of iOS, they will also make appropriate considerations for other platforms too. The ultimate result of this should be a better experience for users. And, if users are getting a better, tailored experience then we all win.