The issue isn't skeuomorphic vs. flat design. Let's reframe it to be about the inclusion of affordances and constraints. What makes a tool easy and intuitive to use is the careful attention given to both enable and restrict the user from performing a set of actions. When a user clearly sees what he/she can or cannot do, they understand the purpose of what's in front of them. Gradients and dropshadows help with that, but even ignoring these aesthetic qualities, we have a whole host of other concepts to utilize, like consistency, proximity, structural heirarchy, and more conceptual digital analogs of real world entities.

Let's compare apples to apples: the iOS home screen to that of Windows. Let's go further and ignore the aesthetic differences, like gradients and dropshadows. What are we left with? The iOS screen has a table of app icons, all consistent in size and alignment. It's easy to see that at the highest level, these are all applications I can access. Let's look at Windows, more specifically the screenshot in the blog post. We see no consistency in size, and further, that grouped set of minicons on the left are of a confused relationship. 3 are music apps, and the fourth looks like maybe text messaging. The iOS apps are laid out in a way where a user can easily tell what is tappable from what is not tappable -- "this is an actionable element in a sea of inactionable whitespace." Contrast this with the billboard-like layout of the Windows Phone UI. You are bombarded with colors and pictures and icons, mere millimeters away from one another, leaving a user in confusion and sensory overload because it's difficult to isolate the various elements. The iOS app screen has an icon and a text label for every single app. The Windows Phone does not. It almost seems like tiles are arbitrarily assigned to be little/big or to have icon-labels/photos. After playing around with a friend's Lumia for some time, I'm still confused when I stare at the screen of a Windows Phone.

I'm not trying to spark an Apple vs. Microsoft debate. I'm trying to show that stripped of all gratuitous skeuomorphism and subtle aesthetic qualities, UIs can still be usable given they clarify to the user what they can or cannot do. I could've done the same mini-analysis with an Android home screen compared to a Windows one and Android would've come out on top for many of the same reasons.