As I see it the I-pad is not competition or replacement for PC, laptop or I-phone. While it resembles the expected computer tablet it isn't designed to fill that niche. It is aimed at the various readers like Kindle. To this they add a few I-phone like applications.
The smartphone, pc, laptop, netbook markets are all mature and saturated so the only way they could sell a new product is to invent a new market.
Its pretty wasteful, you have a device that can't replace any others so you have one more device to buy every few years, keep charged, etc. My netbook replaced a laptop so it was a good buy, my laptop replaced a desktop so it was a good deal too. With this its just another mouth to feed.