That may not seem like that big of a deal, but it's a major improvement on Google's previous implementation, which considered a page new each time Google re-indexed it. That means that if a web page was created two years ago but indexed by Google within the last 3 months, it used to show up as new. The new implementation of the date range determines the URL's age by the first date it indexed the URL, meaning that it now works the way you'd expect. If you want to find fresh Google results on a topic, the advanced search just became a lot more useful.
Advanced Search [Google via Matt Cutts via Google Operating System]
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