Unfortunately, there's no central Muslim organization, unlike the Roman Catholic Church, so a ruling by one person doesn't apply to someone else.
What about Buddhism, Hinduism, Sikhism, Jainism, and myriad other religions? They lack a central authority too. However, they do not go around blowing themselves up. The lack of central authority is only a veil to cover the excesses of Islam and is part of a deliberate effort by Newsweek editor, Fareed Zakaria (who is a fundamentalist muslim himself).
There used to be. It was called the Caliphate and was based in Istanbul. However it was dissolved by Kemal Ataturk, the founder of modern Turkey and secularist who changed the Turkish language from being written with Arabic script to being written with Latin letters, forbidding Turkish men from wearing beards, and forbidding Turkish women from wearing head-scarves. It's similar to if Mussolini had dissolved the Papacy. The restoration of the Caliphate is one if the Islamic fundamentalists' goals.