iOS7's transition to flat design was behind both Android and Windows 8, and clearly followed them. I think the point the author is trying to make is that Apple, the biggest proponent of stylized, squeomorphic design moving to flat UI behind Google and Microsoft was really the final defeat of brushed metal and rich leather in UIs.

> squeomorphic

This is a beautiful typo of skeuomorphic. It makes it feel more squicky.

iOS 7 was one of the last major hold outs so Apple adopting a flat design approach after Windows 8 and Android could be considered the culmination.

Less than 25% of the mobile market is hardly a "major hold out."

It depends how you look at it. Worldwide you are right but Android dominates largely due to the availability of cheap handsets (most of which aren't running the latest Android with the modern flat design style).

In the US iPhone is 40% of the market and considering that 80=90% of users have upgraded to iOS 7 the number of iOS users that are using the flat design compared to the number of Android users with flat design is probably a lot closer than market share would indicate.

Also, although they have less than 25% of the market they are still the second largest manufacturer which in my opinion makes them a 'major hold out'.