To be more specific on my original point: musicians are looking to create a sound. Perhaps that sound has distortion (I rather like that sort of sound) or is overdriven. But that's cool--audio enthusiasts are looking to reproduce a sound that has already been generated and committed to recorded media. Accuracy is (or should be) paramount. Therefore, you don't screw with the speakers to make them any given impedance with the end goal simply to be to change the impedance!
And if you don't think there aren't other 4 ohm speakers out there, I'm sorry, but you simply haven't looked. Magnepans spring to mind as excellent speakers that are 4 ohm (nominal), and, incidentally, are much harder to drive than M80s. I believe the old Dunlaveys were 4 ohm, as well.
