Soundtrack albums (taken directly from film tracks) are problematic. For starters to avoid sounding too distant and reverberant in movie theatres, the sound is recorded very flat (with little reverberation) - the albums sound brittle and boxy.
One fix tried in the 1960s was to add reverb to the albums. This only made them sound hollow.
Another approach was to re-record the scores for the albums (Capitol did this with OKLAHOMA!, CAROUSEL and THE KING AND I.) This gave the best quality sound but was expensive and nit-picky collectors whined that the performances on the albums were not exactly the same as heard in the films.
By the 1970s, multi-track recording meant that different mixes could be prepared for album release and use on the actual film soundtrack.
The recent trend to having singers in musicals sing live on the set re-opens old wounds: In the case of LES MIZ, the singers are filming to a piano track with a full orchestra added later. Obviously a soundtrack album puled from the finished film will have all the noise of movement (footsteps) and sound effects mixed in. That may or may not make for a pleasant listening experience. Re-recording the score from scratch woudl prove very expensive, and although the film is hitting theatres at Christmastime and is expected to be one of this season's big hits, will that translate to CD sales especially when fans already have so many other recordings crowding the shelves. Do we need every scrap of the underscoring preserved on CD? Perhaps a single CD of the key songs would be a welcome alternative. (I don't really think we need another multi-disc set. If you want the full thing get the DVD/Blue Ray when it comes out.)
Cast albums are NOT "soundtracks."
Live theatre does not use a "soundtrack." If it did, it wouldn't be live theatre!
I host a weekly one-hour radio program featuring cast album selections as well as songs by cabaret, jazz and theatre artists. The program, FRONT ROW CENTRE is heard Sundays 9 to 10 am and also Saturdays from 8 to 9 am (eastern times) on www.proudfm.com