Penny,
I haven't listened to this yet - and I will - but I would just chalk it up to one of those ironic contradictions that life is full of. Who would ever figure Dennis Rodman and Kim Whatever-his-name-is from North Korea, as being big buddy-buddies. It's a 'go figure' situation. Boulez explains that he simply wasn't exposed to Mahler in France. We have to keep in mind that Mahler was still the providence of 'experts' and enthusiasts in those times. He simply wasn't standard rep'. His music was a huge challenge for most orchestras in the '40s and '50s, and his music would still be hugely challenging today, if it weren't for the fact that prospective orchestral players have to know ALL of their Mahler excerpts before they ever take an audition.
As for Darmstadt or Donaueschingen music, what's there to say? The vast majority of concert goers simply don't want to hear it. I actually think that Boulez's best works will probably survive. They'll never become popular, but there will always be enthusiasts who'll drag them out from time to time. Then again, there were probably plenty of people who said just that about Mahler's music.
Anyway, I'll give this a listen soon. Thanks for posting it.