Eldartford, my cutting lathe has a set of 'pre-emphasis' modules that are in fact the inverse RIAA curves- if you put their output into a phono preamp, the result should be flat.
It sounds to me that what you are getting at is that not all cutting systems are created equally, not all mics are neutral as well, that sort of thing, and you are absolutely correct.
However, you might be surprised but the cutter manufacturers were actually quite concerned about getting the pre-emphasis correct, to the point of hand-picking components to make it so. The same is true of any high end phono preamp manufacturer; after the hand-picking process we wind up with a substantial stack of unusable EQ components!
Raul is absolutely correct in saying that EQ errors of only 0.1db can be heard and he also gave the correct reason why- its a spectrum, not a single frequency. That makes a huge difference to the human ear.
In the end, this makes it possible to evaluate components used in the recording process, such as mics and recorders. Although 0.1 db seems like its not very much, it **can** be measured quite easily, and the math for generating the EQ networks is well established.
I have seen at least one manufacturer claim that due to other errors, RIAA EQ is not important. IMO such a claim is rubbish and if a manufacturer says that to you, turn around and run as fast as you can!
