Siri–the semi-intelligent virtual assistant feature–has been available on the iPhone since the iPhone 4S launched with iOS 5. However, Siri did not work with the iPad until the iPad 3 came out with iOS 6, and it still doesn’t work with earlier generation iPhones, iPads, or iPod Touch devices.
That’s just one example of the subversive fragmentation within iOS. While almost every iOS device is running the latest and greatest version of Apple’s mobile OS, the available features and general experience vary widely from one device to the next. The highly-touted Passbook feature works with all iPhones and iPod Touch devices, but not on the iPad. The Panoramic picture feature of the camera app works with newer iPhones and iPod Touches, but not the iPad.
I've only been one iPhone model behind, at the most, so I would get most of the iOS features of a new update. I always felt the fragmentation issue with Android and iOS was more a developers issue and not a consumers problem.
It is weird that new Android phones can come with older versions of Android. When considering an Android phone I looked at the Samsung Galaxy S4 and the HTC One. The HTC One comes with Android 4.1 whereas the Galaxy S4 with 4.2. The difference, from what I understand, are features I would enjoy. I could hold out hope that the HTC One would eventually be updated. But how long would I have to wait?