Not all manufacturers devote the same attention. As you point out, some will address specific issues on a movement without addressing a full service. But Patek do not do that. If a watch comes in, it gets a total and thorough service. Not all manufacturers adopt this procedure and not all manufacturers have the same quality controls.
If a watch comes in for service and is fully serviced in 1 week, it may or may not have received thorough and professional attention. Quick is not the Patek way. Thorough is. It has certainly been my experience that although Patek take time to do a service, the work that results is very high quality. I can make that statement as I have experienced about 10 different services from Patek in the last 2 years and a number from other manufacturers....and to be blunt, the Patek experience and work has been superior. so, I guess i am drawing my impressions from experience. That doesn't mean to say that the process is faultless or free of any problems. Problems can arise....as I said in my first posting.....and it then remains with the manufacturer to make the customer happy.