As a designer the take-away I get from this article and what I notice is that “Clean” is what is in. Flat design may one technical way that a clean design is achieved, but it’s not the only way as “Flat Divides” alludes to in his post. Clean can be done using gradients, shadows, or flat shapes. Apple hasn’t fully embraced “flat” but rather still uses glows, shadows and the like but there design still appears simple, elegant and clean. Microsoft went completely flat in their design rendering but the effect in windows 8.1 in particular is played out as busy. There is no apparent color theme, but rather a rainbow of colored squares, the effect is not quite as clean. -And I say this as a bigger fan of Microsoft and Android devices than Apple’s offerings.
I would summarize the current trend as “Clean”, not “Flat”. In contrast the design of the 90’s was over embellishment, I feel this was a result of people displaying their technical prowess as digital design was new as it related to websites.