Radio people are the mediums harshest critics. We obsess on fidelity, EQ, loudness, compression, clarity, saturation and all manner of engineered audio nuances. Good airstaff are just as fixated on their own performance. The smoothness of delivery, the tone of their voice, their intonation pronunciation etc. Pros do not say "um."
Together these two groups create the smooth sound of commercial radio. I do not mean that it's inherently better, or occupies some moral high ground in radioland. Even casual listeners can spot an amateur when they cough, rustle paper rustle, and tap their pencil. But the single biggest clue is the chair drag. A chair in a broadcast booth should not squeak. Beside that, when the mic is on one should not hear it dragged out from the counter. Sit down BEFORE you pot up the mic! BEFORE, BEFORE, BEFORE! The same goes for the mic boom.