The reasons I bought first, an iPod Touch, then an iPad, is that first, no small-sized Android (or other OS) seemed to exist without requiring a smartphone voice and data plan (they want to sell me a huge number of voice minutes, when I use perhaps 8 minutes a month). I used to have a Sony Clie, and loved it (it died).
Also, I could not find all the apps I wanted on an Android device. For example, there are still no good astronomy apps available for Android, certainly not at the level of some of those available for iOS. There's no 800-pound gorilla of a single company urging developers to write/convert apps for Android.