There are many types of computer user, but there are two key ones for this issue; the content producer and the content consumer. The producers will always need a laptop or desktop, you really can't even write blog posts properly on an iPad, never mind a smart phone. Consumers only need internet and a touchscreen. The new 'app' revolution is aimed at the consumers, and that makes perfect sense, the vast vast vast majority of people are consumers only. -Eóin
this is it in a nutshell - the idea that appliances like ipads or 'smart' phones provide anything like portable computing is patently ridiculous.
These things are largely gimick, and they are only successful where the end user doesn't require a portable computing solution.
Sending emails, (inane) tweets, playing (lame) games, watching video. listening to music, reading documents, browsing, or updating facebook do not (IMHO) qualify as computing - try running a big spreadsheet or database, or drafting a substantial document, or coding and see how far you get (or how long your patience holds out)
You could probably draw a parallel with consoles - I've never been a fan, but I know several ordinary households that have versions of ALL the available platforms, apparently because each offers something the others don't (though a single PC could provide all of them and then some...)