iOS 7

The only interesting criticism I've seen of Windows Phone's design language is that by eschewing most forms of visual affordance, it erases a lot of distinctions between actionable and non-actionable elements onscreen. I don't personally see this as a good or bad thing, though; it just requires a different set of conceptual tools to build affordance.

Just look at the first five pictures at the blog post:

1) The left part shows just apple logo. The right one shows a man smiling.

2) The left part contains no pictures at all - just some text, and the right part contain a picture of a nice girl.

3) Both sides of the picture contain a girl smiling. But the girl on the right is definitely looks more open and bright. Heck, even the teeth on the right photo seems more white.

4 & 5) The fifth picture(ios7 collage) contains more smiling people than the fourth picture(ios6 collage).

I am pretty sure there is no coincidence.

Absolutely. I don't understand how so many people are focusing on the highs and lows of the UI but are ignoring serious UX problems like the one you pointed.

Apple says "Nothing we’ve ever created has been designed just to look beautiful. That’s approaching the opportunity from the wrong end." but then they change the perfectly readable Messages screen to a less readable one that has the only advantage of arguably looking better. And it's not the only problem IMHO.

On that screen used to be a send button that invited interaction. You look there and you know that it's "actionable". Now in the new version there is no button, only a gray text with "No Perceived Affordance" that looks more like a description than an "actionable" element. The most important "action" on that screen happens when you press a gray text on a gray background!

And the call screen? On the iOS6 one it was easier to read the name of the person who is calling because the white text is above a black overlay giving it enough contrast. On the new one the text although bigger is lighter (as in less bold) and is directly on the image. Light backgrounds (sky, clouds, etc) will make the text barely visible. Also how can I reject a call? There is nothing on that screen supporting the second most important functionality that is expected from it. Even accepting the call is now more complicated. The size and position of the elements makes more sense now but the text is lighter (less readable) and it's now more complicated to accept a call: before you only needed to touch accept, now you need to slide.

The home screen: even ignoring the aesthetics that I personally don't like, it's undeniable that the text is much more readable with iOS6. The small border and shadow made it readable with virtually any background. Also the icons were easier on the eyes, the new bright colors tire/irritate the eyes more. Also the relationship between icons and the functionality they represent was already hard in some cases. For instance for someone that didn't know Safari it was not easy to tell which was the browser and which was the compass from just the icons. Also the photos icon was not obvious at all and the Music vs iTunes Store icons are almost the same with different backgrounds but now it got worse: none of the exisiting problems got any better and at least reminders, settings and game center got worse.

Of course there are a lot of screens that got better imho. Music, contact view, the calendar, clocks, compass, weather...