Strangely enough, only yesterday was I reading through the Restek website (the manufacturer of my pre-amp). What CEO Adrianus Elschot writes makes a lot of sense (copy/paste the German into Google Translate): while they do measure their equipment not only during the design phase but also during the manufacturing process, they also listen to each unit extensively.
Elschot states that measurements allow for an objective evaluation of product quality and product consistency and minimises sample variation In addition, each unit is listened to by several employees, on different days, and in different locations because each such analysis is dependent on the listener's mood and form on the day. Of course this business model can only work for small-scale manufacturers.
This combination of objective measurements and subjective evaluations both during R&D and during manufacturing makes for a very compelling argument that one needs both in order to make a judgement on a piece of equipment, whether it be as a manufacturer, a reviewer, or a customer.
As an aside, I believe Restek, Krell and other high-end manufacturers who encourage the sustainability aspect of our hobby by ignoring the trend towards planned obsolescence and offering servicing and updating of older gear deserve a shout out.