They all do 10" instead of 7" because Jobs said so. Stupid.

What God Jobs can achieve does not necessaorily mean others can. 7" is the golden size; anything smaller is too small to be productively usable (such as smartphones); anything larger is too large for handheld (such as iPad 1/2).

A smartphone is handy for some quick communication tasks; a 7" tablet is as portable/pocketable but can do much more serious tasks, on the go or in a sofa.