The PC is the correct form factor for getting work done by humans. Mobile devices are not.
I'd say, instead, that the desktop and laptop PC are the correct form factors for getting done the sort of work that you do when seated for a long time. There are probably people whose work is sometimes done while on the move and for which a desktop PC is obviously not going to work and for whom a laptop PC might not work very well; consider, for example, somebody managing a construction project who might need to look things up, enter data, do some calculations, etc. while on site. I suspect that a mobile phone would be the wrong form factor for them, but a tablet might be the right form factor.
I'll actually give you a primary source, real life example.
I'm a paramedic, every single patient for whom I have responsibility of care for, I have to generate documentation for. Up until about 2008, that meant actual paperwork, about then, the industry as a whole being phasing in electronic medical records. To the business office, they're great, because billing the patients, and keeping the records is much easier, and for me, the end user of the system, it's great because, especially when you're using a touch screen and a properly designed program, the computer is much faster and easier to use than a pen (especially for me, my handwriting sucks balls.)
Up until this point, and I imagine for a while into the future, the solution of choice has been to use the Panasonic toughbooks that will convert to a tablet form factor (CF-18s,-19 etc). The touchscreen is necessary, because we actually use it to collect signatures (quite aside from the fact that stabbing at options on the screen can easily cover 99.5% of the use cases), the portability was of course necessary, because I start my paperwork in the pt's house and finish in the ER, the keyboard was necessary because I have to type up a narrative for each pt, and the ruggedness was necessary because we beat the hell out of our machines. e problem is, even the older machines are WAY more powerful than we need, not to mention being heavy as hell (remember, I have to hand these to 96 yo pts to get a signature.)
These EMR suites are starting to be developed for tablets, both iOS and android, and the market is starting to come up with workable ruggedized tablets. nce we get over the industrial inertia we have (which is surprisingly significant, given how agile we're supposed to be), we're going to move to tablets with some sort of external keyboard (at a guess, at odds with the ruggedized tablet, the preference will be for keyboards cheap enough to be effectively disposable), and it will be the right solution for us.
No, my biller and office manager will still be using a full blown PC, but in the field, not so much.