I thought it was the portability and size and ease of access to apps (the ecosystem around the device) that makes the iPad successful. All of these things are

I thought it was the portability and size and ease of access to apps (the ecosystem around the device) that makes the iPad successful. All of these things are possible because of the restrictions in iOS. For example, the lack of a filesystem forces apps to have a more simplified data access mechanism[1]. The good battery life and response time comes from the fact that the OS puts severe limits on what each app can do. [1] - There's an escape hatch of course, with something like Dropbox