Here's an interesting read. The takeaway was that the recommended intervals are fine only under normal operating conditions.
http://www.europeanautotech.net/tech.../engine-sludge
There's as much to be found online advocating more frequent intervals as there is for advocating extending the intervals. So, for someone who spends a lot of money on their car and plans to keep it for the long run, who cares if they choose to spend a few extra bucks here and there on extra oil changes. I don't since I will no longer keep a car to 100 or 200k+ miles, but can definitely understand why people would.