We noted recently that Facebook's list of newly approved "Strategic Preferred Marketing Developers (SPMD)" — client companies and agencies who qualify for early participation in beta ad products and other advanced looks at cool new stuff — contained some apparent omissions.

Some of Facebook's most prominent clients weren't on it.

No one we talked to wanted to go on the record about this topic. But privately, executives familiar with Facebook's ad business confirmed that the social network does indeed play favorites with its ad clients, alternately rewarding or punishing those it does or doesn't like.

To put this in context, in the media business, it's common for sellers to be extremely solicitous to their advertising clients. Dinners, drinks, and free tickets to sporting and arts events for buyers are the norm.