The Tony Awards are perhaps the only night of the year when fans of J.K. Rowling, Bruce Springsteen and Tina Fey can find cause to unite.

There is a reason: Broadway has become a place where major talents from a wide range of fields, including young-adult fiction (Ms. Rowling), classic rock (Mr. Springsteen) and comedy (Ms. Fey), have turned as a way to extend their reach. The development has translated into record box-office grosses for Broadway, although critics have expressed concern that some of this season’s high-profile...