Broadcasters used the cart machine for years. The first units used a transport from Viking of Minneapolis. It was not designed for broadcast, but consumers favored the "8-track" over the "4-track". The Viking-style deck would have gone away, if not for broadcasters. Over time, various manufacturers modified and strengthened the basic Viking deck, and then others developed a different and much more beefy transport to play the carts.
With CDs, however, consumers accepted the format and it became the standard. The transport continues to be available, and has been used without significant modification for years. Tear apart some of the different CD players and you will find the same transport. When I was a peddler, we often had the conversation about whether to spend $1,200 on a CD player and get it repaired on occasion, or spend $150 and replace it on occasion.
While most stations have extensive CD libraries, I would venture to say that the CD players are very lonely these days. For $100 you can buy a hard drive that holds over 10,000 songs (.wav).
