Interesting read.
I think that behind the "skeuomorphism vs. flat design" discussion there is a different prioritization of valid design principles.
- Flat design focuses on: not replicating mechanical artifacts (e.g., no need to limit calendar apps to the one page per month limit that exists on paper), and removing excise (no leather stripes).
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Skeumorphic focuses on: making things obvious (i.e., something clickable should look clickable), and respecting conventions (especially those that users bring from how things work in the real world).
Pau