Since the difference between 40-45 Hz is negligible, the difference in low end frequency response will have nothing to do with 1 sounding brighter: "I think we could expect it to be because the LNT is voiced to go lower (40Hz vs 45Hz)."
Without wanting to derail this with too techical waffle that I only grasp slightly, I think McNach is not indicating that 40 Hz is dub territory per se.
The fundamental in the 30-40 Hz range you feel more than actually hear. The predominant energy comes from 60-80 Hz range and probably the octave above (hence a low B at 30.87 Hz will still sound good on a 40 Hz cab).
Coincidentally double 20 Hz = 40 Hz, which may be what McNach was referring to when he mentioned 'dub".
But really we are getting into territory where we have some real specialists on the forum (BFM, Alex Claber) that will be able to provide much better input than I would be able to.