I would guess that "Islamist" is probably not a widely understood term outside certain circles, e.g., the blogosphere, those familiar with the work of Daniel Pipes, Martin Kramer, et al. It would not surprise me to learn that Sebastian Usher thinks "Islamist = Muslim", which would explain the use of the adjective "radical". But what can you expect from the BBC, Reuters, and others of that ilk who use the terms "soldiers", "militants", "fighters" and "activists" to describe barbarians who murder civilians in buses and shops with crude anti-personnel bombs, or pump bullets into a pregnant woman and her 4 children at close range?