I suspect this actually increases exposure and traffic to SO. If you look at the quoted data it is definitely not enough to decide if that's the right answer. It's going to get you to click through as you really need context, like vote ups, compare/contrast with other answers, look at context of question, etc. I think it's a bright move on SO's part and they really do control what they share with Google.

It's basically a free ad for SO. Smart.

Also, it could be that Google is paying SO to do this. You never know.