I am just telling what the Apple people tell me over the phone. All I can gather from this is that the vast majority of the employees at AppleCare are under trained and full of dung. If your system has a problem as such, then why would they want you to try re-loading and all the junk they get you to do in the name of diagnosing the issue.
If what has been said is true then either Apple doesn't understand how their own systems work, or they are simply relying on the customer to be totally naive for how things are supposed to work and hope that using technical jargon to the unknowing will just get them off the hook.
Your point of the fragility of the Mac OSx and how it seems to require constant reloading to get things to work. One would believe that things should not break on a monthly if not weakly basis, but I have found that to be more than true. What is sad however is that every re-load you roll the dice that something new will be broken in the process of fixing something else. It may be the idea that apple just wants people to need to constantly upgrade to newer hardware as they feel their older hardware is just too old and breaking down too often. And some say that Microsoft Windows is bad. At least you know that you are required to re-install every 9-12 months to keep the system running well.