Technologies are not well thought out.

Podcasters host MP3s on a web site. So any time a listener grabs it, they download it from the web site. In the case of someone with a limited bandwidth hosting plan, it is very possible for the bandwidth to be exceeded. Events like a major software provider (iTunes) and service provider (iTunes Music Store) suddenly listing the podcast could result in the creators exceeding their bandwidth. There is no facility for distributing the podcasts so that any one locationo bears the brunt of the downloading.

Oops.

Apparently no one anticipated the possibility of hundred of thousands or even millions of computers grabbing the RSS feeds associated with blogs.

No one predetermined someone would actually want to send an email under a forged or even non-existant identity.