Any module which supports the "ISearchable" interface can provide a list of the "items" in that module to the core (so for example, Announcements would provide the list of announcements, HTML/Text would provide the HTML content of the module, etc.). The Core then stores these in the "SearchItems" table, for use by the search engine at a later time.
So, because of the fact that the SearchItems table contains a list of items gathered from various modules as well as the time they were created, it makes a perfect source of data for a "What's New" module. In fact, SearchItems is also used to generate RSS feeds for modules too, if they want.
You could use Reports to query the SearchItems table, and use the XSLT visualizer to lay it out the way you want. Or, you could tweak the "What's New" module. I'm not really familiar with "What's New" so I'm afraid I can't be much help there, but if you have questions about using the Reports module to query SearchItems, I'm happy to help as much as I can!
Hope that helps!