Why Radio?
Nowadays, the term 'radio' is used to describe any audio service that provides continuous realtime audio to the end listener. Strictly speaking 'radio' traditionally referred to an 'over the air' transmission method but in practical terms, whether you use traditional radio waves, streaming, or any other 'transmission' method, it is still all 'radio' as far as a listener is concerned!
The key thing that differentiates radio from other 'on-demand' audio services is the perception of a live, 'in the moment' service (even if it is actually automated). When you listen to a radio station, you are listening to something that is happening 'now' which is often what drives people to keep listening. It's also a "shared" experience - you are listening to exactly the same content as all the other listeners, making you feel like you are part of a larger community with shared interests.
That does not mean that 'on-demand' should not factor into your plans. The 'On-Demand' generation expect to be able to consume entertainment on their own terms, so often a combination of live output and on-demand content is a winning formula!