From Scripting News:

Neat search script for the Radio aggregator, made the post above work, even though the Times article it points to is more than a week old. Read the comment at the head of the script to learn how it works. For geeks only.

Note this sentence in the comment:

It reads the XML archives stored locally, looking for a story containing the "lookfor" string.

In other words, Radio already has a persistent store. It's just not exposed to the user... yet.