They are the only people that currently have religous and political leaders encouraging violence against others. Oswald and Ray were lone nut cases - they were not egged on by their government.
How many countries outside of the middle east have fund raisers for people who strap bombs on themselves and blow up other peoples kids? How many religions teach their followers that members of other religions need to be killed and that the killer will be rewarded?
Terrorism exists around the world--including here from extremist groups. There are some "Christian Identity" type groups here that encourage violence, for instance.
I do agree that terrorism and violence is more prevalent against Muslims than other groups, though.