"lectures may not exist in the future"

What would I listen to in my car streamed by bluetooth from my phone? Radio? No way.

What might happen is someday, someone is going to record "The Ultimate verbal explanation of a PDA automata" or whatever, and then for the next 500 years that'll be The One that everyone listens to. It hasn't turned out this way in books because of legacy analog media combined with desire of publishers to maximize profits. Imagine if you could just download the Feynman lectures on physics. Aspects are out of date, but still going to be better than the local talent.