It seems that monophonic radio recordings are distributed at all kinds of bit rates and sampling rates. I guess because fidelity isn't too much of an issue, With lower rates they can pack more on a CD.Very few MP3 capable CD players like "alternative" bit rates, and fewer like less than 44KHz sampling rates.
iRiver makes MP3 CD players that accept just about anything thrown at them (down to 8 kbps / 8 KHz)