Not buying it. Most people can deal just fine with spreadsheets, which are the epitome of high density UI.
What people don't deal with well are badly designed UIs which present illogical controls and information.
And yes, high whitespace UIs results in people seeing less confusing shit on the page, but only because it's now spread across 3 pages, not 1.
If you're dealing with a hundred people in an office, then the vast majority can probably deal with a high-density UI. Because they are there for work and the UI - and more importantly the concepts underneath that UI and the mental model it requires - will be related to the stuff they already know.
But if you're dealing with an audience of millions who are trying to pass the time, or using apps or parts of the system that they rarely interact with, or have no real interest in the device, then a high-density UI will be extremely intimidating. They have no mental model of what is being represented on-screen - and if it's casual usage, they have no desire to spend the energy to learn that mental model. What they will want is the device to have two big buttons saying "do this" or "do that". Which is why the iPhone's grid of icons endures - "I want a bus ticket", "I want the camera", "I want to watch a video".
Personally I think the hardest part of UX design is ensuring the model presented on-screen matches the model that the user is expecting.
Which has two implications - firstly, it's entirely audience dependent and secondly, the further the UX model and the actual underlying model diverge, the more cracks will appear while people are using it - so you have to design from the bottom up for that given audience.
The audience of MS is corporations, yet they design for touch screens. Who uses a touchscreen 8 hours a day ?
If typing weren't such an important part of my job, I probably would too. There have been times when I've not been writing much code and then I rarely touched a computer. For calls, meetings, sketches, quick note taking, planning stuff out, audio editing, things like that I much prefer an iPad.
And, perhaps most importantly - if they don't learn, they can be removed. Big difference between UI for work, and UI for fun. You can design differently for a captive audience. This can be used for both good and evil (also see: Government websites).
I bet you're thinking about people who have used spreadsheets before. You might even be thinking of people who use spreadsheets weekly or daily. Try putting them in front of a new user, and you will be shocked.
As someone who has performed many usability tests, I can only think of one person who said "I wish this was more dense and complicated", and that fellow sticks out because he is the exception who proves the rule that almost everyone wants it to be simple and above all clear. Most of the time, people just want to know what they should be doing next, and everything else is a potential source of confusion.
I’m kind of upset with myself that i find this statement so profound. I mean it’s such an obvious framing (sadly only in retrospect in my case).
Probably time to re-evaluate that prior.