As a serviceman it ALWAYS annoyed me that when you went to measure a voltage or look for a particular part on a board all you found was "TP2" or "C34". I always thought that was next to useless unless you had a circuit diagram and even if you did you would have to refer to it to find exactly WHAT TP2 or C34 was. All electronics manufacturers are guilty of this not just pinball.

There is simply no need for it - it's plain laziness, nothing more. Where board space permits I always add information that I believe aids servicing or adjusting. Build quality is a different thing. I guess it must be weighed up how much extra the brass resistor spacers cost, the time it takes to add an extra screw in a heatsink to make sure it can never spin out of place and so on. For this board these (and many other) little extras probably add $1 to the board cost - that's all.