Broadcast stations need to keep recordings of their output for legal purposes. (CCTV security systems are almost the same problem.) The typical approach at the moment is use long-playing VHS videotape; this requires someone to physically change tapes, and does not provide fast random access.
The obvious solution is to computerise it; this'd also allow a radio station to provide instant access to bits of its archive. (Indeed, many of them already do this -- the DNA Lounge is a club that does the same thing for its audio recordings.) The basic idea would be to slice incoming audio up into chunks, then compress the chunks with an appropriate codec and dump them to disk. It's vital that data not be lost, so RAID should be used for local storage and data should be pushed to an offsite backup as soon as possible.
It'd be feasible to offer offair recording -- and public archive access -- as a service for several radio stations, using multiple physical sites for better redundancy. Even a stereo soundcard would allow two stations to be recorded simultaneously in mono, but a multitrack card would make this more convenient. A central archive could provide direct access for regulatory authorities, or could even be run by the authorities themselves; this should work out cheaper than the individual stations keeping their own archives (and would avoid the problems of stations missing bits of their archives and needing to store them).
I'd guess most of this has already been done; doing bit-perfect digital archives is certainly something like BBC R&D have looked into.