What has happened is that along the way in destroying the personal computer, the iPhone has become our defacto personal computer, not the tablet. But we use the iPhone much different than the iPad. I think like the PC the iPad is now a niche item meant for specific careers and occupations. As you would use the iPad if you’re a graphic designer, you would use the PC for computer programming and computer aided design. Meanwhile, I’ve heard people compare the iPhone to a portable data centre.
One thing that I think will exasperate the iPhone sales: airlines. It’s likely the TSA/FAA will ban laptops from being operated on flights. They could easily include tablets in the laptop ban, meaning only smartphones will be allowed to work during the long transcontinental flights.