Stupid speaker test question...please help a n00b

Spartanmorning, One reason is that few manufacturers who use more expensive underhanged speakers would have clear advantage. No incentive for everybody else who is using overhang drivers to publish distortion. The other reason is that speaker distortion is not only performance at particular frequency and sound level but also at complex signal (music). Non-linear membrane action and membrane bending at higher frequencies creates intermodulation distortions. Speaker also has different phase shifts at different frequencies and presents complex load to amplifier that is difficult to measure. Specifying distortion at particular sound level and particular frequency driven by some perfect lab gear would not make much sense. There are few people on this forum who know speakers much better (design them for living) and I hope they will comment on this interesting thread.

"I have to say I find this field of 'hi-fi' quite frustrating"

You're not alone. We are here to learn.