Maybe him want delay the release for better divide the time between pre-rtm and rtm, without create a long interval between this two.
simply consider that OS development is not a machine that puts out an OS for testing every 10 days or so. It is all made by humans and delays can happen when bugs are heavy or other circumstances are responsible for
But is always a beta, they can make a real fast ring for release a new build every week, instead of wait all this time
Careful now. Posting build numbers like that freaks people out around here. Talking "end of the world" freak out.