Maybe the producers that use the LFE channel for music are following a similar rule: they want all the lower bass to come from a single speaker.
I wouldn't bet on that, though. My guess is that a mix that uses the LFE channel is "cooler".
Here I go again - getting in a rat hole with the LFE channel.
For music, the mains will have all of the low frequency information even if an LFE channel exists; so the single speaker theory doesn't hold true and is why for music, the LFE channel doesn't really make sense. In the end, if you have a good bass manager somewhere in your system, the LFE doesn't matter; as the bass manager will make sure all of the low frequencies go to the correct speaker (given you have it set up correctly.) Unfortunately, the "coolness" factor may be the only valid reason for a .1 channel. But once you understand how works, it is not so cool anymore.