Anyone out there adhere to the "new rig every six year rule?

In a somewhat related vein, I'm amazed at the number of people who have a one or maybe 2 year old multi hundred thousand dollar rig and are in the process of getting a new one - why? If I had the money to do that, I'm pretty sure I wouldn't do that. Sounds like too much of a headache with all the things that can be or go wrong with new ones, even the most expensive ones.