His point is that if 90% of the users were color blind, the accessibility options would be enabled by default. So, in accordance, if 99% of people use a wide screen, task bars and window decorations should be to the side, not top or bottom, by default.
It goes well beyond that. I can't make the bookmarks or tabs on the browser go down the side even though that would save a bunch of space vertically. Windows/Ubuntu/Mac OS all use the titlebar at the top of the window and waste vertical space even though horizontal is more in abundance and has been for at least 15 years. When you step back and look at the interface its all vertical aligned, everything is top to bottom and yet vertical space is the most precious and least wasteable, why waste 50 pixels on a titlebar and tab bar? The fact fullscreen exists for some apps says it all about the OS waste of that space.
There are a few programs that do this well. NLEs for video usually use horizontal space for the timeline and they get much better horizontal use than just about anything else I use. Photo editing software often puts toolbars on the side but even though inkscape does do this it still has a toolbar even with the tools and properties either side. But websites are mostly vertical and waste most of the space a lot of the time as are browsers. The OS wastes a bunch of vertical space where horizontal is available and the taskbar/app bar is about half of the problem.
