While you assessment of the browser situation some years from now, is far less depressing than the picture Paul Irish paints, you're ignoring his point that not

While you assessment of the browser situation some years from now, is far less depressing than the picture Paul Irish paints, you're ignoring his point that not only will we have to deal with different versions of IE, but on top of that, we need to regard all of the different render-modes/document-modes that will possibly be integrated in future IE versions, for the sake of compatibility. It is by that line of reasoning, that Paul Irish makes the assumption that we'll be targeting some 72 different "browser versions" in 2020.