Just as a clarification, "Copying is the most common way (and the current .NET way)" is not the case - .NET GC is generational but it does not promote through generations by copying.
"I'm not 100% sure what he did say" - this makes me a little worries. What wasn't clear exactly? I've hoped that the GC history from 48:50 covered "the Lisp part" good enough.
I believe it is not difficulty level problem but the fact that due to value types existence in .NET it was ok to live without escape analysis for so many years (like @cpeterso also pointed out).