Perceived averages are highly inflated, especially among the top end.
Most students over-estimate the abilities of the state. Also, as mentioned, BoS mainly attracts the more higher ended students, as evident by the amount of accelerants and students sitting 'higher order' subjects and students from selective schools. I mean, why would an average student bother going on a forum with a bunch of nerds - the internet was designed for facebook and porn, not study
Anyway, I still think that the cutoff should be in the 50s. I don't think it'll be like 2001 where it goes down to the 40s and referring to some of the earlier posts, the board doesn't have a set amount of students it wants in each band. It determines a level which is the standard and then they take it from there.