Personally, I don't think "aggression" in a general sense is ever truly cured, but I do think that through careful training and desensitization, a dog's triggers can be eliminated, thus eliminating the aggressive response to those triggers. Is it a cure for aggression? Not really. I see it more as maintainence - it's something you need to keep up and continually monitor if you don't want the behavior to return. When you live with an aggressive dog, there is no point at which you say "okay, mission accomplished, no more aggression!" and immediately release control of the dog. It's something that always needs to be kept under control, and I really don't think it ever goes away entirely.
Some types of aggression are, IMO, impossible to eliminate and very difficult to control. A dog with an inherent predisposition to aggression is always going to have the instinct to behave aggressively in certain situations, and it's hard for conditioning to overcome instinct. I wouldn't ever expect a guardian breed not to protect its territory, just like I wouldn't expect a sighthound not to chase things, or a Border Collie not to work livestock.