The look, it's not a-changing much
Although numerous similarities exist, the first years of iOS' existence clearly haven't matched OS X's exactly. For example, many new iterations of Apple's desktop operating system include distinct visual styles; the Finder, Dock, window title bars, and more have all undergone dramatic redesigns over the years.
iOS has far fewer universal elements to change, and thus hasn't seen nearly that amount of visual change at an OS level. On/off toggles changed slightly with iOS 5, but the general look and feel of the iOS home screen and various interface elements is virtually unchanged.
To date, most of iOS's visual evolution has been limited to Apple's default apps; Calendar, Address Book, and Safari's looks have changed a bit over time, but you can count systemwide design changes on one hand. Perhaps that will change over time.
iOS 5 continued Apple's trend of taking iOS and making what was already awesome even more so. Can Apple keep up the pace with its mobile OS?
With Tiger, Apple clearly felt the pace of annual updates couldn't be sustained. Its followup, Leopard (10.5) wasn't released for two-and-a-half years, affording Tiger by far the longest run any iteration of Mac OS X ever held. Will iOS 5's successor not arrive until April 2014?
Fear not. Apple hasn't announced plans yet, but I would expect iOS 6 to arrive before the end of 2012.
For all of iOS's shine, the mobile OS remains nascent. Multitouch is still a new interaction paradigm. Apple's accomplishments with iOS to date are impressive, but you get the feeling that the company has only scratched the surface of what iOS can do.
On the Mac OS X side, Apple faces just one major competitor--one it knew it couldn't unseat on the marketshare side. And Microsoft Windows rarely pushes desktop operating system innovation forward; rather, it consistently plays catchup with the Mac features.
On the iOS side, however, Apple dominates in profit share, and its market share remains quite competitive with Android. Other touch operating systems, like Windows Phone and WebOS, haven't yet achieved much market penetration--but both have still succeeded in clever touch breakthroughs on their own. The point? More competition ends up being a good thing for Apple and iOS customers alike; it motivates (and perhaps forces) the company to continue improving and refining its own touch interface.
Sure, Android borrowed heavily from iOS, but with at least a tiny handful of features, iOS has since returned the favor; one need look no further than iOS 5's Notification Center for a prime example.
After nearly two years, Leopard begat Snow Leopard--an update that almost exclusively addressed under-the-hood improvements. And it was just under another two years before Lion first roared--bringing numerous iOS innovations back to the Mac.
With iOS, however, Apple's still just getting started.
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