Reading this, I think he's very right, especially about Windows 8.
The part about the iPad mini might be correct too, we'll need to test and might need to adjust some apps. But if developers have followed the guidelines for touch sizes, things should still work quite well with no changes.
The article is much more correct about Windows 8 and tablets/desktop. The iPad mini would have a 2" change in size vs the 20" difference between a tablet and a desktop. I can already say from just using the previews a little that most Metro (Windows 8 Style-UI*) apps look huge and silly on my desktop, where the same app on a smaller-size-screen tablet would look far better.
Windows has gotten away with all sorts of screen resolutions and sizes by being Windowed. This is the download window for GetRight 1.0 from over 15 years ago. On some monitors it was bigger than others, but its one size worked on them all. In the years since, the graphics have gotten better, but the window size changed very little. And it worked on every install of Windows--the first versions even worked on Windows 3.1.
Yes, some Windows and Mac programs can go fullscreen, but the program has the choice. If it doesn't fit that way, it can be disabled easily by the developer. (I'd only ever used developer tools with lots of lines of text at fullscreen size. I've never used any program on my Mac in fullscreen mode.)
Imagine a calculator app that must fill the whole screen. On a phone it'll be perfect. On a tablet, it could be made to look good and fit nicely--but then imagine that same app blown up on a desktop. It would be totally silly.
Same for a clock app; Apple finally did one for the iPad in iOS 6, but some of the things look a little silly even at that size. The tiny little minute selector in the middle of the screen for the Timer for example. Now again, imagine that blown up on a 27" desktop screen.
* Microsoft does such a good job picking cool sounding code names, but then runs them all thru some corporate filter. How XBox didn't become "Microsoft Windows Game Console Live" we'll never know.