Of course that's one part of it - as I said, familiarity impacts productivity, "don't fix it if it ain't broke" etc. But I really think that visual cues are useful. Take multi-level default menus Peter griped about - they really look like dense columns of newspaper print on cheap recycled pulp - two shades of grey on another shade of grey, with no separator between the main menu and submenu. You said that icons would make it too cluttered - I agree, but more contrast and clearly delineated submenu wouldn't.
I understand you didn't invent this - I am finally getting used to Win 10 UI. OK, at first glance it does look "cleaner". But, how does one know which window has focus? Well, one doesn't, except by the merest hint of a shadow it "casts" on those below it. And if the window has panes, it is almost impossible to tell them apart from proper windows. The same is happening with web sites - light grey on even lighter grey - I often have to select the text to be able to read it (or use one of those "reader" browser plug-ins that remove all clutter and use sensible fonts and colors).
But enough of us grumpy old men complaining... :o)
(BTW, for the life of me I cannot find a way to enable code folding symbols. Folding (from View menu) works, but nice old intuitive symbols are not there. How do I get them back? )