I don't believe DA engines have any more problems than others. Their owners just seem to like to brag about the quality service though which is probably justified. That quality service is factored into the price though. When you're proud of a product you own, a bit of bragging can be in order from time to time.

Looking back at DA engines I've owned or had my hands on, different engines were sent back with bearing problems, reed / intake problems, ignition problems and one needed updating before it was ever run. All fixed at zero cost and as others have stated, various improvements were made while the engines were in for the requested repairs. Later on, I repaired a couple of DA 50s at different times. One needed a new ring because the old one was seriously eroded near the exhaust port and the other one needed a new reed cage / housing. Pretty much the same kinds of service parts and requirements all engines need from time to time so nothing special there.