For a shop mechanic there's little extra payoff connected to building the best wheels, good enough and as fast as possible is where the money is.

An average looking wheel used for average(That's real-life average = low mileage, not BF average...) riding by an average guy has a whopping huge safety margin in its design. For such a rider you can get away with a lot of things w/o having any issues with the wheel. Poor tension, broken spoke, manually straightened rim etc - not a problem. What this means is that it's easy to lull a wheel builder into a false sense of skill, as he's simply not seeing enough failures to get him to question his build and hone his skills.

Then someone like you comes along, and things begin to go wrong. There are plenty of tricks that can be used to build a stronger-than-average wheel, but you need to ask for it, and the builder needs to be skilled enough to deliver.