[nollidge]

Right, and I think the key part of envex's statement is "by now". Meaning that in this stage of history, the ubiquity of pseudo-3D graphical interfaces means people are able to pick up on the subtler affordances of flat design. And as you say, the bolder colors and flow help, but even with that I don't think this sort of design could have worked 10 or 20 years ago.

It's sort of like how art went (very roughly) from realism to impressionism to abstract art. People got used to the meticulous accuracy of paintings, and so artists cashed in on that cultural context to start getting abstract.

People get UI mechanics enough now that a huge rectangle with monochrome iconography is all you need to convey "clickability" to the average user.