This was brought up by netaustin at #448000-9: Big, Over-Arching Sitemap Architecture Discussion (tm):
"# Google News provides a namespace to extend the Sitemaps.org XML file for their purposes. Can we address this?"
I looked more into this and according to http://www.google.com/support/webmasters/bin/answer.py?answer=34654&topi..., there are actually four "sitemap extensions" that Google supports:
The news one in particular would be useful to a lot of Drupal sites out there.