I think thought that with regards to Les Miserables, I don't think it was a case of a new cast sans Francis and Colm. I think that there were a fair amount of alterations to the score that merited a new recording. The intro/overture is different as well as different tempo changes. They also shortened Little People for the Broadway cast and the song I saw Him Once, which came before A Heart Full Of Love was gone at that point.
I know that Disney tried with Beauty and The Beast, to release a cast recording of every international cast. When they realized that financially speaking, it didn't make sense to have multiple english language recordings of the same show, they stopped doing it.
Wicked didn't do a London cast recording because the show opened up with Menzel.
I think that, because cast recordings aren't very profitable, if a show is a transfer on either side of the pond, producers try to not make another recording if they don't have to. Considering that Miller was in both the London production of the show and now with it on Broadway, they might feel that it isn't worth recording the score anew.
"If you try to shag my husband while I am still alive, I will shove the art of motorcycle maintenance up your rancid little Cu**. That's a good dear"
Tom Stoppard's Rock N Roll