cypherdoc changed his mind because Gavin did presumably. Gavin did because it was easier to do this as quitely as possible than to try to change the laws of arithmetic.
Both of them know that it's the exponential growth that is the critical element here since it is pretty certain to sink Bitcoin eventually. (Actually, cypherdoc may or may not know that or may or may not care much if he can make a buck in the interim.)
Quite clever wasn't it to start with 20MB then appear to compromise with some bloc of obscure "Chinese miners" who want 8MB and quietly slip in the exponential scaling.
The hypothesis that Gavin simply fucked up the argument+ arithmetic seems stronger to me. He seems to be the best bet as 'benevolent dictator' since Hearn has burnt way to many bridges. It wouldn't do to have the main man be so incompetent if it were a concocted plan.