Simple--the War in Iraq doesn't really pose any personal threat to them, the way the Vietnam war did.

Under the heading of "wrong lessons learned" when Nixon instituted the lottery, everyone whose birthday fell above the magic number knew they were safe--It knocked the wind out of the anti-war movement, which is just what it was intended to do. If a general conscription was implemented, the streets would be full of protesters in a New York minute--thats why it hasn't happened, and won't happen.