The image on the left is the iPhone calculator, and the image on the right is the Windows Phone calculator:
Neither gets it quite right.
The display on the left does seem more inviting, but notice that it has more buttons, a useless conceit held over from the limitations of physical buttons. Also, the one on the left has smaller, harder to read buttons, but the shading does add some depth to the interface, and the difference in color of the display bar is helpful.
The display on the right is easier to read since the buttons and the fonts are larger, but the buttons could use some more distinction, whether it be shading or depth or highlights on the edges.
Realism in the user interface does have its place. As mentioned in the Slate article, it provides an intuitiveness that may be very important for the less technically literate (think of the yellow legal pad feel in iOS Notes). But these literal interpretations of real-world items should not be taken too far. The fact that these applications are virtual means we are not constrained by things such as lighting or viewing angles or physical space, and skeuomorphic design should take advantage of that lack of limitations while still referencing the most familiar and salient landmarks.
Larger buttons with more shading and distinction of boundaries would provide a better display than either of the two shown above.
