You need the same mix of experienced talent working in the UI as you do with traditional "serious" stuff. This is where Apple is simply ahead of everyone else.
Not only does Apple not shunt n00bs at the UI, it actively hires extremely brilliant people to do UI invention/R&D.
E.g., consider the CV of the (obviously brilliant, IMO) "Up and Down the Ladders of Abstraction" guy, Bret Victor (1).
That's about two lightyears removed from "UI is boring and easy; make the junior programmers work on it while we do the algorithmically hard stuff on the backend."
(As an aside, Holy Shit is BV impressive and refreshing -- incredible tech chops combined with awesome aesthetic/design sensibilities, all wrapped up in a humanistic focus on usability...just, damn.)
(1) http://news.ycombinator.com/item?id=3099595, http://worrydream.com/#!/cv/bret_victor_resume.pdf, and http://worrydream.com/Bio/