Absolute weight matters much less in running than cycling up mountains. No runner is fighting gravity as directly as cyclists rolling up and down a mountain.
10k is easier to get closer to a 100% effort your first time/first few times out than a marathon. Experienced runners still take years to fully show their marathon potential, even after they are aging in the wrong direction.
I'm impressed by TD's 10k. Serious question: does anyone have any photos or know what shoes he is wearing? Same with Yate's marathon? I will also say that road races can be mis measured, but haven't looked into what event TD ran at.
For a non-runner, the new carbon fiber shoes can really be the missing piece. They are purported to impact running economy, something a non-runner but trained cyclist would have the least of but be most ready to capitalize on improvements in.