News, for example, is not exactly a stellar example of something built for podcasting. News expires almost instantly and therefore the time shiftedness of podcasting looses almost all of its power. Credibilty is another factor that podcasters are still struggling with. The main stream media news sources just plain old have better credibility than Jon's News Hour. Lastly, big stories take big bucks. I forget who said it, but someone once wrote that Watergate could not have been broken by a blogger. It took time, money, research skills, connections, and a lot of other things that many podcasters and bloggers don't have.
Some MSN news outlets are offering podcasts, however. I think that those will continue to work because they address the last two points. Because MSN produces daily - or more - shows, the time shift is minimal as opposed to a weekly update or news podcast.
The other way to look at it is in terms of evergreen content. Since podcasts can remain online forever, they should contain content that's relatively useful and interesting forever. Daily news expires by its very nature making the archives almost useless.
Are ther any other topics that don't work well for podcasts?