I understand the idea of recording the songs at a different time to the shooting of the rest of the film, but these are musicals. They're about songs. Debbie Reynolds and Eddie Cantor are singers. The director of "Singin' in the Rain" specialized in musicals (although he may have used a musical director). My gut feeling, for what it's worth, is still that these are in-jokes.

Anyway has anyone noticed any other examples like the two we started with? I'll post more as we find them again. I'm sure eventually we will. Cheers, Joy