I seem to be relatively alone in this, but I find the connection between alcohol consumption and incomes pretty obvious stuff. That may be because I live in DC, where all social interactions occur atop pints. When I was spent a Summer here at age 20, I considered writing an article for Reason lamenting the invidious discrimination of drinking laws, which really does bar interns and younger folk from making the professional and personal connections that can propel their career forward. As it is, there's an interesting causality question -- are the same qualities that make someone successful and rich the reason they make a lot of friends and field a lot of bar invitations? -- but this seems like a rather standard example of social capital in action.
To put it starkly, if Ezra Klein and eZra kLein both work at The American Prospect, but only Ezra goes out drinking at The Black Rooster when his coworkers and editors want to share a pint, Ezra is going to have more influence in the magazine, more rapport with the higher-ups, and will be favored for promotions simply because he scores highly on subconsciously important evaluations of intersocial pleasantness. It's little remarked on and probably unfortunate, but resumes and job interviews actually offer relatively little information on potential applicants for positions, particularly because the most telling portion, references, will often be hand-chosen for effusive praise. For that reason, applicants with an actual foothold into the employer's social circle will be favored, simply for their ability to form a genuine social impression. And to make things even more unfair, he and all those social capital amassers will be at lower risk for STDs...