[blehn]

Sure, while browsing the web, you explore and click most of the time, but there are plenty of instances when you need to type: a query into google or a url into the address bar, logging in to websites, commenting on a blog post, responding to an email. These things will have people reaching for their laptops in no time. Even if these are specifically for browsing the web from the couch, why not just use a laptop? They even have built in stands (the keyboard) so that your arms don't get tired holding them up.

Also, I'd imagine that typing on a touchscreen tablet PC is considerably more cumbersome than on an iPhone, since you'd only have one hand available.