Perhaps the pause was indeed a sign of quite, respectful admiration before being replaced by an aggregated applause - the two-minute pause at the end of M9 was well earned and well respected by everyone in the hall as seemed right.
I've not been to a classical concert for some years now so perhaps my memory of the etiquette involved is patchy, I don't know. If I'd attended Bernstein's performance of Shostakovich' 5th with that spectacular finale I'd have been up on my feet within seconds however, so perhaps it's all about the particular piece of music that's being played - and how well - that determines the individual and collective response.