Minimalist Affordances: Making the right tradeoffs
Learnability is not an intrinsic property of a UI; it is a function of the context (cultural and otherwise) in which it is used.
Makes you wonder how understandable any UI would be to someone from 50 years ago — or 50 years in the future!
(Really enjoyed this post by Lea! And this linked thread on UX StackExchange was intriguing too.)