[mercer]

I think the iPad did well partly for the same reasons that the iPhone did well despite not being the first 'smartphone': an easy, slick user interface and decent/great hardware. The fact that the iPad had tons of apps (which the iPhone didn't) probably helped.

Another factor might be timing. The iPhone, and by extension other smartphones, laid the groundwork for making it socially more acceptable to use these kinds of devices. I vividly recall being a bit embarrassed to pull out my geeky 'PDA' in the dumbphone days, and I felt much less of that when I got the iPad (while none of the people around me had one).