I did this because the JWT properties are abbreviated (see http://tools.ietf.org/html/draft-ietf-oauth-jwt-bearer-04#section-3). I feel that instead of having abbreviated versions and non-abbreviated versions floating around in the code, sticking to 1 form would be less confusing and neater. Having said that, that does rely on the reader of the code reading the draft or doing some research.

If you feel the non-abbreviated versions would be better, I am happy to update them :)