I agree with you it probably isn't economical, at least not yet. But the reason for wanting it is for the power supplies to be arbitrarily interchangeable.
One of the big advantages of the move towards micro-USB charging cables for phones, for example, is that in my house we now have several adapters spread around the house, and both my wife and I can now charge our phones at any one of them, despite having different brands.
I can see the advantage, but I still would argue that just having some DC power standard like USB will always be more economical and practical than trying to build "do it all" supplies to work with all gear despite the absence of a standard.
One of the big advantages of the move towards micro-USB charging cables for phones, for example, is that in my house we now have several adapters spread around the house, and both my wife and I can now charge our phones at any one of them, despite having different brands.