Flight idle and ground idle
What are the reasons for having different idle speeds for jet engines in different flight regimes? I note that there is a ground idle, which seems to be about 25% N1, and a flight idle, which seems to be around 40% N1, and both seem to be automatically set for idle in recent aircraft (I suppose pilots of older aircraft set these speeds manually?).
I've read of two potential reasons for the difference: (1) Higher idle speeds at high altitudes reduce the possibility of a flameout; and (2) flight idle is designed to match the drag of engine nacelles so that an aircraft can glide in a descent with the drag of the nacelles "erased."
Are these the real reasons? Are there others? Is the notion of flight idle and ground idle common to all jet aircraft, or only certain aircraft? Are there other idle speeds?