Your points are very valid and really crappy service on a MK 15 (the tech dropped the piston and nicked the seating edge - but would never admit it) and a desire to get maximum performance from my regulators is what led me to become a tech.
As a tech I agree it is difficult to tune a customer's reg to the peak of performance as a few months or 20 dives later when a bit more of a seating groove develops the odds are good it will develop a freeflow. If it is an adjustable second stage it is no big deal as the diver can adjust it a little harder and resolve the problem (and in fact never realize what is happening or that there was aproblem to start with) but if the reg is non adjustable, the customer comes in bent out of shape over the inconvenience of having to come in for re-tuning. Mail order service is even more problematic as the customer ends up paying shipping at least one way if not both ways.
So...I see no real problem with customers knowing and learning enough to tune their own second stages. It is not rocket science and with 10 minutes of training and under $30 in tools they can do a good job with it - with 20 minutes of training and $50 in tools they can be great at it and know when to bring it to a tech in for more serious work.
