There many places in the world where it is not possible for larger companies to map them. These can be for economic reasons as is the case for Black Rock City (the temporary 40,000 person home for Burning Man). Or for political reasons as is the case for Iran and countries such as China.
As I mentioned the other day Google greatly improved their map coverage of Iran via user contributions through their Mapmaker program. These user contributions were applied just a few weeks ago. Here are before and after screenshots of two Iranian cities. The before shot was taken on September 22, 2008; the after shots were taken on May 18, 2009.
Mashhad (Before and After)
Tabriz (Before and After)