Well a PG-13 film can have one non sexual use of the "F" word. Anymore than that and it's an "R". It's not surprising at all that's what the film got and I'm sure it won't hurt it in the slightest.
The studio could've easily changed the language to make it PG-13, so the fact that it got an R probably shows the studio believes this rating won't hurt the film.
The surprise to me isn't that this got an R (the rules, as explained above, are crystal-clear and JERSEY BOYS surely must have more than the automatic R requires.) The surprise to me is that we the public still continuously empower such a backwards rating system that permits effusive violence and sexual innuendo but places strict limits on language, among other criticisms of the MPAA.
Words don't deserve that kind of malarkey. They're innocent, neutral, precise, standing for this, describing that, meaning the other, so if you look after them you can build bridges across incomprehension and chaos. But when they get their corners knocked off, they're no good anymore…I don't think writers are sacred, but words are. They deserve respect. If you get the right ones in the right order, you can nudge the world a little.
"The studio could've easily changed the language to make it PG-13, so the fact that it got an R probably shows the studio believes this rating won't hurt the film."
Or, they are just ignoring/disregarding the crushed dreams of all the teenagers trying to learn about the origin story of Frankie Valli and the Four Seasons without a guardian...
It's only an assumption that the 'R' rating was given solely for the use of the 'F' word. Anyway, it is what it is. "JERSEY BOYS" isn't exactly Disney material. I don't think the rating matters either way in making or breaking the film.
Tangentially related: the South African/Asian tour is currently in Kuala Lumpur, and they cleaned up the language. (I didn't think that would ever happen.)
You do realize that with an R rating, it suddenly becomes 'hip', right? (The rating might work in its favor with certain audiences.) Musicals are often viewed as 'squeaky clean' and having one rated R may tap into a different audience.
For what it's worth, there is subject matter (SPOILER ALERT): The death of Frankie's daughter and his treatment of his wife, that are not exactly PG material.