Going back even further, blue-grey-white has been around forever. I still have an older Windows NT machine that throws out plenty of blue-grey-white screens. Granted those are easier to read since they haven't yet switched to sans serif fonts. Anyway, I don't think blue-grey-white is a new idea.
I don't disagree! However, it's the way it's been implemented (poorly) recently that stands out, IMHO. Salt has been around forever too but the minute a pizza maker poorly implements salt by over-dosing it in levels beyond what's been "typical" and "best in class" for decades, it's noticed!! Today, I contend that flat design using light blue/grey on white is far-overused than before ~2013 and in ways that no longer feel "right." When I go back to using an old iPad stuck on iOS 5, it's obvious Apple still used grey/light blue then too (in more ways than I recalled, actually) but the WAY it was used/implemented within the overall UIx was so very tasteful, useful, intuitive, that it didn't slap you in the face to where you noticed it. Once iOS 7 landed and borders/buttons and other context-enabling UIx cues were virtually obliterated, the over-reliance of light blue/white on stark white stood out rather obnoxiously. For instance, using blue text to indicate actionable/pressable whereas, before, a "button" would light up blue only after you pressed it to indicate it was pressed. Or, before, light greyed-out text/buttons/options indicated "not available" while now, light grey text (in place of a button) often indicates an option to press but which is just currently not pressed. The whole UIx world was flipped to suit Jony Ive's (and others') minimalistic trendy styles while completely undoing decades of UIx development based on learning & human nature, requiring re-learning all these less-intuitive (IMHO) UIx cues virtually completely bathed an overdose of light blue/grey as the prime theme instead of using blue a bit more sparingly and using light grey to indicate "non-options." Then it unfortunately bled into website and app design.
That's my story and I'm sticking to it. Go look at an iOS5/6 iPad/iPhone/iPod or Mavericks (or earlier) OSX and see how blue/grey is certainly used but was used SMARTLY instead of blindly across the board.