Well, doesn't "business is business" mean that all business endeavors are equal? But they don't seem to be. Some may call selling cocaine, business. But I think many would consider this type of business dishonest, scummy, rotten, or evil in some way. Contrast this with a business that is honest and doesn't base its sales on selling illegal substances, and you may see how "business is business" appears to overgeneralize.
In the case of wars, it is often the case that one war is more justified than another, and so to say "war is war", seems to overlook that.
The peculiarity here is that of mistaking an abstract notion (like war or business) for a concrete, singular notion. Saying "The American Civil War is The American Civil War" is different from saying "war is war". This is because the former notion is concrete, and the latter notion is abstract.