The exclamation point works overtime on Broadway. Consider the classical musicals Oklahoma! (1943), Oliver! (1960), and Hello, Dolly! (1964). These enduring smash hits seem to have cemented the exclamation point as a typographical stand-in for jazz hands. Since then, the Broadway exclamation point has been used extensively in ironic and non-ironic configurations on and off Broadway. I Do! I Do! (1966) doubles up on the exclamations, as does the avant-grade, non-musical Oh! Calcutta! (1969). Hollywood adopted the exclamation point both for Broadway adaptations and for original musicals (e.g. Moulin Rouge! (2001)). The Broadway exclamation point is so common-place, that it's surprising when musicals eschew it (e.g. Chicago (1975) would have been an obvious candidate for the bang).
One of the main uses of the Broadway exclamation point is as an abbreviation for ": The Musical". Whereas to suggest a movie version of some story, one appends ": The Movie" to the subject (see Jesus: The Movie), to suggest a musical, only an exclamation point is necessary, or maybe also an abridgment to one word a-la Oliver! (see Microsoft! and Godot!).
Compare with the exclamation points in Yahoo!, Jeopardy!, and Airplane!.