Incidentally, I know people who use an iPad as their primary/only machine, and it works for them. Of course, this all depends on what someone uses a computer for. Today, with an excellent version of Office available for the iPad, even moderately complex work can be done on an iPad (or an Android tablet, for that matter). Unless someone's in a field that creates highly complex document or conducts complicated analysis, they can probably get away with using Office Mobile, a Web browser, and a few other productivity apps. Let's not forget that there are many, many good apps available for iPads.
This isn't to defend the iPad, per se. I just get bothered when people define for other people what a piece of technology can do. And it's also kind of silly to argue that iPad > SP3 isn't a viable upgrade, when the SP3 is intended to serve as a tablet _along with_ serving as a notebook. The way Microsoft themselves have positioned it is that an SP3 is an upgrade from _both_ an iPad and a MacBook, together.