Odd that GiveWell is not even mentioned.
My guess is they simply haven't heard of it. I left a comment on the article here mentioning GiveWell and existential risks; if you guys want to click the little "recommend" link that would be great. (First you'll have to click "Log In", then "Log In with Facebook", then go through the Facebook popup, then tell WSJ that you want to skip linking your Facebook account to your nonexistent WSJ account. But this should be no problem given the high number of expected lives you are saving, per Bostrom's paper.)
http://online.wsj.com/article/SB10001424127887323372504578466992305986654.html
Apparently a hedge fundie made 4 billion and is giving most of it away to what the WSJ describes as a "moneyball" approach to giving.