Jeff, it's more like: When you air programming that appeals to only a fringe of the fringe element, eventually you will chase away all the donors.
There's lots of stand-alone non-comms that have consistent donations, mainly because they have programming that tries to appeal to a larger segment of the population. In the last "public" PPM month (prior to only publishing 6+ of subscribers), which I think was March, WBAI had a cume of 96k. Could have been 98k, but really what's the difference when you have a full market signal smack in the middle of the dial in NYC and you can't get more than 100k people to listen!!
They're a victim of their own craziness. I don't know if an AM is going to be any better for them, since there are some big electric bills and lots of upkeep, especially if it's a multi-tower DA such as WADO. I can see them letting the vines grow up the towers...
What would be interesting is if WNYC swaps the AM + cash for it, puts WQXR on 99.5 and puts the spillover programming from 820 on 105.9.