Shadorne - My friend has the same theory as you do regarding the processing of IR stations. Perhaps that's the answer.
Yes - radio stations have compressors and limiters and all kinds of stuff to create their "house-sound". Depending on the target market they can enhance various aspects of the sound in a way that suites their listeners. For example, a Rock Station will typically target commuters in their automobiles and compress the music to get it to sound loud over the car and road noise. Meanwhile a late night show may enhance the bass frequencies and smooth the highs for a laid back relaxing smooth sound at lower listening levels...