It is all about voicing not revealing the spec. Now if your speakre required a low or high LCR spec good to know. Other than that just listen to it.
Well, sure, sound is the most important thing. Nonetheless, I think it's useful for manufacturers to release this information for several reasons. As you said, some speakers (e.g., electrostatic ones) come with recommendations, and one might like to start with low L and C. (Low R should be key for any speakers.)
Second, though it's often difficult to correlate what we hear with measurements, I think it's worth seeing what measurements can tell us and where they're lacking. We'll never get there if specs aren't even available.
Third, when I looked for specs, I noticed that some of the manufacturers who don't publish them are not shy about publishing technobabble saying their cables are better. Doing that seems particularly dubious if you're not willing to reveal the actual physical properties of the product. At the very least, it encourages the perpetual cries of "snake oil!".
