[Cheesehead]

I wouldn't say mixers are 'bass managing' music in Theatrical mixes.
As Bob and Garret say, you can't rely on the lfe channel being reproduced and the main speakers are full range anyway.

That doesn't mean that the sub isn't used for music though.
Just as it would be in the 5.1 mixes of music as delivered to the mix stage.

I haven't heard a dvd or bluray before that is 'bass managed' in the mix, (ie all the content is consistently sent to the sub), I'll have to look at Deadpool and see what you mean.

It sounds like a very bad idea and I can see your problem, double bass management in a home theatre, ugh!.
Of course the near-field mix and certainly the DVD/Blu-ray mastering, isn't necessarily done by the mixer themselves, so I suppose weird things can happen.