[ricardobeat]

That's affordance, not skeuomorphism.

From Wikipedia: a skeuomorph is "an element of design or structure that serves little or no purpose in the artifact fashioned from the new material, but was essential to the object made from the original material"

The gradient and shadow on buttons are not just ornamental, they serve the purpose of conveying depth, and consequently that they afford being pushed (also, real-world buttons are usually a solid color).

[jhermsmeyer]

I think we are splitting hairs here, but I agree that what we are talking about is affordance.

The reason why I use the term skeuomorphic in this context is because there are those who believe that what you and I believe is affordance is actually superfluous and ornamental.

What else is flatland design if not a complete rejection of the value of drop shadows and gradients as affordance?

[goldfeld]

Gradients and drop shadows on buttons are usually modelling solid color real world buttons; design uses an imaginary light source coming from above to mimic the way our world usually has a lamp or the sun shining up there.

[ricardobeat]

That's precisely what makes them affordances: gradients and shadows are modelling real-world clues, not mimicking design features.