The 30mm Bushaster automatic cannon is replacing the aging Bofors 40mm
(FKA Pom Pom gun) on the Ac-130s--or at least a rearmeament was approved citing the age of the bofors and the increasing dificulty getting and dealing with aging ammo.
Also cited is the "hard Maintaince" of the 25mm guns on the Spooky II fleet (follow up are known as Specters).
As to the difference between the Diplaced 25mm and the 25mm on the IFV Bradley, I and not yet clear.
The article only states that the "25mm is difficult to maintain in the air" and actually cites army development and deployment of a 30mm.
This i, I am guessing, not in the power class of the 30mm "Avenger" cannon on the A-10. Although the latter is becoming a bit "long in the tooth".