I hate how lazy authors think there is no fragmentation for apples products.
There are many different versions of the iphone (2G , 3G , 3GS , 4 in white / black with different memory sizes) with many different versions of hardware, throw in a few apple TVs, oh and dont forget the 4 different ipod touches and a couple of iPads.
There are many different versions of iOS with some devices not being able to be updated to the newest. 47 different versions (http://en.wikipedia.org/wiki/IOS_version_history , assuming I've counted correctly).
13 (iphones) +11 (iPods) + 4 (iPads) + 1 (TV) = 28
28*47 = 1316 possible variations of iOS products. Thats a lot of fragmentation
(Note I've got it a bit wrong in that 47 versions of iOS are not available for older products so the real number will be quite a bit lower - but its still high).