Where do you draw the line? Let's say I'm a core developer on Rails, am I not allowed to use Rails then? What happens if I contributed 1 line of code to Rails, does that negate it then?
And obviated by the judges having no easy way to learn and isolate which "part" of the app they're testing, and how such compartmentalization goes strongly against human psychology.
I don't pretend it'll be "perfect", but it should let decisions fall (noisily) around what we think of as "fair" (since we're all running that assessment through the same hardware) which is really what we're looking for.
<rules-lawyering-participant>So I get my buddy/silent-partner to develop my cool and unique API beforehand and sneak it unannounced onto a relatively anonymous public Github account before the comp starts, but close enough to the start date that no-one else will have even heard of it yet.