*sigh*
1) How do you know WSDK is even encoding for PPM?
2) Not only do 6+ PPM numbers mean nothing to radio stations, they mean even LESS to religious and ethnic broadcasters. I can't speak for WSDK, but most religious stations often don't rely on advertising, but on listener gifts. All you need is a small but dedicated listener base that's willing to pay for very specific niche programming. Just ask Bob Bittner, he does it with WJIB and WJTO. Why does WJIB never show up in the Boston PPM's? Because it doesn't encode. Why doesn't it encode? Why bother?
Minority formatted stations operate in a similar fashion. All you need is a small but loyal base of hispanic-targeted businesses to advertise... and trust me, they're not buying "the book." Listener base may be small, but it's fiercely loyal. The station works for specific advertisers to reach a specific crowd.
You could put the most mind-blowing amazing programming on WNEZ Manchester, WLAT New Britain, or WSDK (Blount Masscom) Bloomfield, and the national buys wouldn't be rolling in.
One more time, with feeling. Just because Arbitron doesn't estimate listeners for a station does not mean nobody's listening to the station.