I’ver never heard of an Islamist radical referred to as a “Preacher” before. He sounds more like a “screecher”.
He was a boxer, like Tamerlan, interesting connection.
Probably the confusion is due to the author of this piece. He's using western terminology to describe the person's role in Islam society. It would be like referring to a protestant minister as a "priest". Many of them have similar roles, but would never use the word "priest" since it generally refers to ordained Catholic clergy.
I wasn't sure what the Muslim terminology for "preacher" would be myself, if we're using it like the Muslim equivalent of a Billy Graham or a Fulton J. Sheen -- someone who is not simply the leader of a congregation but known for their public speaking and articulating their faith to others. Most of the Muslim religious titles are more along the lines of degrees of scholarly knowledge and judicial titles. An Iman is the Muslim equivilent a pastor, in that they lead the congregation in prayer at a mosque and they're responsible for overseeing the day-to-day affairs of the Mosque (and even then, many of them appoint someone else to hand the buisness end of it, and their duties differ vastly in Sunni and Shiite Islam... Sunni's make up over 80% of Muslims and their Imans are NOT ordained and NOT considered to be clergy or have any special powers to bless people and so on, they're just educated lay Muslims volunteering to coordinate the congregation)
Someone who preaches sermons about the lesson found in the Quran is called a khatib, and most Iman's are also khatib's. So a well established mosque would have an full time "Imam Khatib". I don't believe they preach outside the mosque though.
Probably "Mullah" (which means "Master") or "Sheikh" (which means "Elder") would be closer to the Christian concept of "preacher" in terms of some prominent public figure. Mullah's have memorized the Quran by heart, recite scripture in public, and give islamic advice to others, and Sheikh is an well respected Islamic leader who organizers others... again, their duties vary considerably from country to country, and whether they're Sunni or Shiite Muslims. Shiites have a much more complex and organized level of religious hiarchy (pretty similar to Catholic clergical titles), with the highest level being an Ayatollah, such as Iran's "Grand Ayatollah" being an extreme example of the absolute highest religious authority in the country that everyone else defers to.