What makes the dilbert funny is because it is true. This thread is full of dilbert's who can't fathom getting "serious" work done on anything less than a desktop/laptop and at the same time there is a whole generation of employees out there (I work with them everyday) who can't fathom tethering themselves to a grandpa box.
I will stick to my granpa box that can actually get work done. While you technically CAN work on a smartphone or a tablet you will be a vast disadvantage to someone using a real laptop or desktop. Ideally you would have access to all of those. If you are in the store and you get an idea or need to check something up, smartphone go!
If you are actually in an office and you have a desktop, laptop, tablet, or smartphone, then your actual productivity is:
Desktop > Laptop > Tablet > Smartphone
A bigger screen, a proper mouse, and a more generous keyboard just means more productivity, no joke comic will change that fact.
The debate isn't whether or not smartphones are displacing desktop/laptop in the workplace but rather the debate is are you going to give up your sliderule after having used it for 20yrs and learn how to use one of these newfangled toys (some might call it a fad) that is the electronic calculator?
Progress marches on, it is the duty of every aging generation to dismissively refer to the younger one's tools of productivity as the next fad.
A calculator is much faster, requires less specialized knowledge (easier to use), and smaller.
The problem with your analogy is that as you go supermobile you give up ease of use (smaller screen, worse input systems) and performance (MUCH slower performance, slower internet). Which is the exact opposite...
A better analogy is that you have the serious workers with their calculators and then those newfangled youth comes along and uses a slide ruler made of gold studded with diamonds that make "cool" beeping noises to impress the ladies (it doesn't work)
The real modern users don't abandon their desktop for a smarphone, but find a way to seamlessly sync them. What I forsee 20 years from now is people carrying a mobile device that does phone, but is also a powerful computer, and it can dock (wirelessly) into a base-station that provides a proper monitor, keyboard, and mouse (and nothing else) to get real work done. Said base station would only have a tower with CPU/GPU of its own if is a hardcore gamer's computer. For the average users it would just be the 3 peripherals.
This is because a tiny 4 inch touchsceen will never replace the monitor, mouse, keyboard holy triumvirate. We will be with it until the day we get neural implants.