It's not a substitute - It's another device with different use cases.
Most people have a resistance to having to own too many devices though. If the iPad doesn't get at least one killer app that really doesn't work as well on an iPhone or a laptop, then it won't go anywhere.
Most people have a resistance to having to own too many devices though. If the iPad doesn't get at least one killer app that really doesn't work as well on an iPhone or a laptop, then it won't go anywhere.