I think one of the main things it proves is:
1. Desire for new shiny things
2. Increase in disposable income
Sure, I can come up with some uses for an iPad, and it's a nice looking device, and, at least in the US, the pricepoint compared to the average income is very low - so people are talking about outfitting their whole family with one.
But honestly, there is really not much of a case for it being a 'must have' product.
It sells well because it's Apple and it has the huge Appstore behind it. It's not really revolutionary nor magical - it's a fairly obvious concept - there are just few (any?) other companies with the 'cachet' that could bring it to fruition.
In my opinion the iPhone was much more of a revolution, combined with the Appstore as a single point content delivery system.