This can't possibly be true. It may be true for home users and hobbyists, but people running business applications need screen real estate and a keyboard on which you can touch type. That's the Achilles heel of mobile, and it's not going away.
The point is, I already carry around a phone in my pocket, and eventually, when I get into the office, I will hook it into my monitors/keyboard/mouse, and work away. The PC cannot keep up, and will eventually be replaced by this paradigm.
Then there's the question of computing power. Recent mobiles look powerful, but that's because you're comparing them to older mobiles and not to desktops/laptops. The MIPS you can squeeze into a mobile will always be constrained by heat, and you're just not going to get anything like the same snappy response you would from a dedicated machine.