I think the reason is that they are "testing" it merely under the guise of it being a user feature.
Once the users become used to it, the real target is to charge advertisers / business fan pages, etc. Hence why it's not using credits, but will become part of the ad system instead. Sure, they'd make money from the users, but the real money would be made from the advertisers.
FB could argue higher fees since advertisers aren't friends. Then all they need to do is apply pressure by scaling back the reach of the free fan page status updates in the user feeds even further. (Since this has already changed to a fuzzy "relevance" black box, it would be easy for them to get away with.)
Edit: To add to that, the initial user acceptance.. There will be less uproar/outrage from introducing this to the users when they know it's just their dumbass friends to blame. Once the feature has widespread acceptance, then the source will be less of a concern, and the advertisers can be brought in. If they brought the advertisers in first, the backlash would be severe. Boiling the frog and all that.