I think Apple would rather people buy a MacBook and an iPad rather than just an iPad and so they've limited it to make that happen even if it means selling less iPads to begin with. They don't really seem to want to make great standalone products but want everything to be tied together which is why even doing something as simple as adding a single MP3 to your music library on an iPad is effectively impossible.

Some of what they did with the iPad was a response to the success of the Microsoft Surface and I don't think it's something they actually wanted to do.