Wasn't that D'Angelo, or did Cheever invest too? According to this it was just D'Angelo.

http://techcrunch.com/2012/05/14/quora-raises-50-at-400m-fro...

It was Adam, not Charlie, that invested in the company.

Adam has 1-2 orders of magnitude more wealth than Charlie outside of Quora (due to earlier/bigger role at Facebook), so it's probably reasonable that only Adam invested.

There's a bug in the back of my brain wondering if the recent round was Adam buying Charlie out.