I also don't think the fact that APIs aren't copyrightable is a clear cut case.

Can you imagine if int add( int, int ) were (or suddenly became) copyrightable?

Perhaps that can be seen as too trivial; but consider something like:

void qsort ( void * base, size_t num, size_t size, int ( * comparator 
+) ( const void *, const void * ) );
[download]

If, every time a programmer sat down to write a function; he had to perform a copyright search to check that he wasn't duplicating a function signature that someone else had used somewhere at some time in the past, this industry would grind to a complete halt.

That is proof by reductio ad absurdum, but the principle holds. And with the advent of IP Trolls, and the general rise and rise of companies like Apple and Oracle using litigation as the first resort rather than the last; it is not so absurd.

Api definitions involve little more than the serial juxtaposition of a half a dozen or so keywords, chosen from a very limited subset. The permutations are finite.

Imagine if writers were able to copyright phrases -- short combinations of common words. It would very soon lead to the situation where it became impossible to communicate in writing at all.

buk_The buk_only buk_solution buk_would buk_be buk_for buk_each buk_individual buk_or buk_company buk_to buk_'register' buk_their buk_own buk_unique buk_prefix; buk_and buk_then buk_you buk_end buk_up buk_with buk_communications buk_of buk_this buk_sort buk_and buk_life buk_just buk_gets buk_king buk_ridiculous.