Perhaps there is one specific detail that attributed to the SQ guys success rate that none have mentioned. I have friends that tell me over 40 SQ Skippers applied for positions. They only took about 8! So what they really got was the cream of the crop. ( by their standards) and not necessarily a " group" that were more culturally adapted to the training.
Just remember there is often much more to these things than the written word ( mine included).