Um no. http://www.google.com/search?q=school+shootings+locations Remember the rural Arkansas shooting by the young boy who had been bullied, for example?
Tons of shootings occur in urban school as well. When I was a substitute teacher in Oakland, Ca. Public Schools from '85-'90, between 2nd and 3rd period at Oakland High School (the school near the College Ave. area near the Berkeley border) a kid was shot to death in the halls.
The yr. before a third grader in East Oakland shot to death a schoolmate during, "show and tell." http://www.csmonitor.com/2006/1004/p01s01-usgn.html?s=t5 One of four fatal school shootings to beset rural America in just over a month, the rampage that killed five young girls raises anew a host of old concerns - about campus security in countryside settings, access to guns by unstable individuals, and "copycat" violence advanced by media attention.
Plenty of rural and urban school shootings here,
http://en.wikipedia.org/wiki/School_shooting
Rampage: the Social Roots of School Shooting (2004) by Katherine Newman
More generally on US violence, Going Postal: Rage, Murder, and Rebellion: From Reagan's Workplaces to Clinton's Columbine and Beyond by Mark Ames (Paperback - Nov 16, 2005) -- Michael Pugliese