To me, the flat UI of Windows 8 looks more like that of a Web site than a vintage Windows version (although I've only used Windows as far back as 3.1; I used Am

To me, the flat UI of Windows 8 looks more like that of a Web site than a vintage Windows version (although I've only used Windows as far back as 3.1; I used AmigaOS/Workbench before then, which shifted from a flat look in v1 to a sculpted look in v2+). In Web design, 3D buttons and rounded corners have been a consistent pain to implement, at least until recent versions of CSS. The usual trick was to have a different background image for each corner, a different repeated background image for each edge, and a flat colour behind the text; all of this would be constrained to line up by a hierarchy of divs. On the other hand, flat rectangles have always been easy, so they could be seen as the Web's "default look" (if we ignore native controls). I see the trend towards flat (native) UIs as a way to blur the distinction between Web sites and native applications. This certainly makes sense on mobiles, where many native applications are just an alternative UIs for Web sites (which might even be implemented in HTML/CSS/JS!). In that sense, it's not so much that desktops are regressing towards the battery-efficiency of mobiles, but towards the lowest-common-denominator of Web UI.