Both would massively flop in those houses.
And I don't think so, it's a long term investment for the theater owners. Frozen is likely to be a VERY long running show - although I would have guessed the same for The Little Mermaid, so I guess we'll see. So, they'll likely make money hand over fist on Frozen at the St. James for the foreseeable future. So it makes sense. And plus, with the demands of design, etc, I'd imagine more backstage space is great for any incoming show, and if they have the ability to do it, why not?
Theatre is such an interesting thing because we've been using these theaters built for vaudeville for years now without changing the interior much, when the rest of the world has change so drastically.
I saw Something Rotten the other night and noticed there weren't a lot of actual set pieces, most of it was all flown in, so they must not have a lot of wing space.