The retention polls are being skewed by the National Guard which has some legitimate gripes. A disproportionate number of the troop types needed in Iraq are part of the National Guard. While most Guardsmen are happy to fulfill their obligations they really did not expect to be away from their homes and job for two closely spaced 18 month tours.
The Army has recognized this problem. It is working on moving these needed occupations into the regular army.
This article states the sample did not include Reserves or National Guard.