Bandwidth is expensive. As a general rule downloading is “cheap” and uploading is “expensive”. Think of downloading as “offloading” the network and uploading as “loading up”.
Using a service like Amazon S3 gives you some advantages due to sharing scaling with Amazon and its other clients.
The easiest way to lower the cost of something like a podcast / streaming services like radio is to use geographically located proxies. This is complicated and expensive. S3 won’t even do this for you. In order to get this sort of “geocaching” you need to hire a company like Alexia to cache your data globally and serve it up to and end user a geographically local as possible. Super expen$ive, but worth it if you are say… Clear Channel and your bandwidth bill is in the $millions / month.
It should also be noted that switching to Amazon S3 or other high end hosting services is not trival. Amazon S3 is not your typical hosting provider and you do not just get an FTP access to an apache server in the traditional sense. Amazon S3 is a framework built and resold to companies who want to use the Amazon infrastructure, the cost to deploy such a solution might even outweigh the benefit of $50k / year. Developers are expensive, also.
There is no such thing as a free lunch.