When the musical “Wicked,” described as a prequel to the “Wizard of Oz,” opened on Broadway in 2003, I had no great expectations for its success.I wondered how it could possibly attract fans of the 1939 MGM classic film starring Judy Garland or devotees to “The Wiz,” a 1978 production with an all-Black cast that featured Michael Jackson and Diana Ross.Therefore, I was amazed to learn that original show had been nominated for 10 Tony Awards in 2004, winning three. It lost out for Best Musical to “Avenue Q,” a very clever …