What you're saying about icons is true, but only if we're talking about desktop software that has major releases only every few years, or software that otherwise uses a very standardized and common set of icons.

That isn't what we see with most web apps these days, including the major ones. There's continual change, including the icons that are used, where they're positioned, and what happens when they're clicked on. If you discover what an icon means and does today, there's a very good chance it'll have changed by tomorrow, if it's even still around.

We're much better off losing a small amount of space, but getting an obvious and unambiguous description when text is used instead of icons.

Also the trend is wrong. Old mobile devices needed icons. But then you have a 1920x1080 screen on a new mobile device, you can read and distinguish truly tiny text quite easily (I'm finding a lot of websites are much better in desktop mode on my S4 these days, for example).

Text works just fine in most applications, because the shape of a particular word is itself iconography.