Unlike the Robert Siciliano, security consultant sees in New York: Even a 25 cent bullet could hit a conventional expensive car "pretty efficient". For stars who earned several million a year, it is not unusual to spend a lot of money for their safety.
http://www.haz.de/Nachrichten/Panorama/Uebersicht/Gepanzerte-Autos-in-Hollywood-so-beliebt-wie-niemals-zuvor