1) ...
2) Your perspective as a developer makes you uniquely unsuited to evaluate the average white collar worker. You are simply not one of them. The example you cite - an exec checking email in an airport (or perhaps reviewing a spreadsheet, marking up a presentation or contract) is *exactly* the vast majority of the professional working world today. And they can - and will - increasingly rely on the thinner/lighter/good enough capabilities of iPads and other tablets.
3) The convention you cite - of sitting at a desk across from a screen (or two) and a keyboard - is a matter of legacy, not optimization. The world's professional workforce is increasingly mobile, and another cycle or two of hardware flushing at major corporations will bear this out. As a coder you are one of an incredibly small number of people (relative to the whole) who really truly needs a "full fledged computer." Most others do not.
4) Add in the cost conscious blue collar world, the developing world, and youth of the world, all of whom are price sensitive (in general) in their own ways, and almost all of whom mot assuredly do *not* need a full fledged computer...and the trend is simply inexorable.
Tell you what. If you disagree, book mark this, and revisit it in 12, 24, and 36 months. The 4:1 ratio you cite will be reversed by 36 months. In fact, if anything, I'll take the Under.
Yep, I can see the future. Millions of mobile professionals zipping about from airport to airport while a few minions sit in their offices working on laptops and desktops.
As a matter of fact, I design software for those minions. And as the poster above notes, your view of the world is remarkably skewed. For every "mobile professional" you cite, there are 10-100 folks sitting in offices working at desks at least 8 hours a day. And despite the hopes of youngsters, the "mobile execs" aren't going to outnumber the worker bees. Not soon. Not ever.
I can hear the howls if I suggested those people trade in their 20" monitors with multiple windows for tablets that would enable them to wander about the halls of the buildings in which they work. But at least they'd be "mobile professionals."
I'm afraid you've been seduced by those glossy ads with attractive folks toting their tablets about....no doubt on their way to parties on the beach with similarly attractive folks.