This reality has led pundits to believe that iPad size is the right size for a touch tablet. But I've come to believe that in just two years, iPad-sized tablets will represent a small minority of the market.

It's hard to believe now, but experts used to argue about whether there was room in the space between a phone and a laptop for any kind of consumer electronics device.

Now it has become clear that there are major markets for two sizes: An iPad size in the 10-inch diagonal range, and a smaller size in the 7-inch diagonal range.

Not only should these two form factors be considered distinct, but in many ways they should be considered opposites. The big one is portable (home, office, coffee shop) and the other is mobile (absolutely everywhere).