The nature of news is that it is constantly developing. For example, we first heard about the Haiti earthquake. Then we learned how its rating on the Richter scale. Eventually, we understood the utter devastation it has caused - and continues to cause - in the Caribbean nation.
Many times reporters update individual stories as they learn new information. As such, it presents a challenge for indexing. Google is addressing the challenge by recrawling news articles to index the changes to an existing story. Many of the updates to an article occur within the first day of publishing. Because of this, Google has set the recrawling to occur frequently during that time frame.
In related Google news, Reader is now allowing users to track changes to websites and pages that don't have RSS feeds. Simply plug in the URL to the "Add a Subscription" option and Google will create a custom feed for that page.
Incidentally, you can plug in the individual URLs of news articles that you wish to keep track of in Google Reader. You'll get a notification of changes if they occur.