We learned from Shawn Coyle that the Israeli Gunships operate at 3000 ft AGL. At this altitude they are out of range of small-arms-fire. In Iraq the Gunships have to fear MANPAD's (man-portable air defense systems). That's why they stay low and expose themselves to gunfire what their armor holds off in the most cases.
This is my own interpretation. So if you know better, please let me know.