Most of the insights available on LessWrong don't require people to understand Bayes' Theorem (or timeless decision theory).

"What you believe after seeing the evidence depends on what you believe before seeing the evidence" is, I think, a decent "layman paraphrase" of (one aspect of) Bayes' theorem that I think people do need to understand. "Don't forget to consider other ways the data could have arisen" is another.

On TDT, I agree; I regard that as more of a specialized AI topic.