I agree with you that theoretically most folks who like Hannity should like Levin. I don't know, but where is Levin on the Talkers Top 100 talk shows? Rush #1, Hannity#2, etc. My guess is, that Mark Levin is further down the list, definitely not in the top 10. There are other conservative talkers like Levin, who all say the same thing as Rush/Hannity/Beck but are considered 2nd, 3rd tier shows (my guess is without the cramdown Levin would be in with that group). Their personality, style, the sound of their voice, etc, can make a big difference. Also, when the show is aired, and on how powerful of a station, what is the lead in show before, etc. I used to like Monica Crowley's show when it aired on WILM, but she's no longer on, so I don't get to hear her except if I catch on tape, when I remember to set up the VCR (which isn't often) before leaving for church, the McLaughin Group, which if I remember correctly is on PBS. Laura Ingraham, I also like, up to a point. She airs on WDEL at night, so it's not a live show, probably not as good of numbers as she might get for WDEL if she were on during the dayparts. Mark Levin airs at 10pm on WILM, so chances are his numbers won't be as high as the daypart shows. But my main point is, just because a talk host does conservative talk doesn't mean he/she will be good, or successful. Same with lib talkers. If WNTP 990 from Philly came in with a strong signal that I could get at work (can't get it at all) I'd probably listen to Michael Medved and Dennis Prager over Beck/Rush/Hannity, but that's just my taste (they'd be more like a conservative NPR talk show in my opinion).
WPHT has a stronger signal, but they do not penetrate the buildings as well as WILM does (WILM's transmitter/tower is in Downtown Wilmington about 4 miles from my workplace - WPHT's is in Philly much further away with more to interfere). I get WILM loud and clear in my building almost anywhere, and can get WPHT very poorly, if I place the radio in one certain place or in a window. So that does play into WILM's favor. Out in the car, both come in loud and clear. But my guess is Glenn Beck is making the difference for WPHT's grabbing WILM's daypart audience as I mentioned earlier for those who can pickup WPHT at work.
CC is using WILM to clear Rush/Hannity in the Wilmington market as they also do with their Dover station, WDOV. WDOV does have Beck as well.