While I respect and admire both of these industry stalwarts, I disagree with their assertions. I do agree with atmasphere that no rational mind would purposely design a speaker to play only one type of music. But that does not mean that all speakers are equally good for all types of music.@br3098 If you have a means of designing a speaker to favor a certain genre of music, its likely that you also have derived a new branch of physics. At the very least you stand to make millions if you can figure out a way to do this. No-one has ever been able to do it before and so currently there are no loudspeaker examples.
On that account the simpler explanation, using Occam's Razor, is that the idea is simply a myth.
The absolute **classic** example of this is the JBL L-100 loudspeaker that has been the rock goto for 40 years. The only problem is, while it is a classic speaker, its not any better at rock than anything else. I find it colored (at least the earlier versions- the new one might be different) and the better the recording, the more the flaws of the speaker are revealed.
Some people say that Cerwin Vegas are what you need for rock as they play loud, but orchestras play loud too and need the same bass response. That bass response is needed for jazz if you're going to get the bass drums right; quite simply what makes a speaker great for one genre of music makes it great for all genres.