It was also a topic that confused me when I came to this forum.
All my books were very clear in that you should leave your beer in your primary FOR AT LEAST 10 days to make sure you remove any DMS or Diacetyl. But never longer then 30 days because thats when autolysis can start.
In reality, they were probobly just being extremely conservative. I suspect autolysis is one of those things that depends on a 100 different factors. Like OG, strain, temp, aeration, pitching amount, time, etc.