Here is the single sentence: All five of Nort Buechner's statements and definitions are too narrow, excluding important parts of the science. Look at them one at a time:
Dr. Buechner is doing something akin to what some people do with art: Saying that Picasso is "not art". That way you don't have to explain what's wrong with it, since it doesn't even fall into your category. (Or saying that Quantum Mechanics is "not physics" as opposed to saying you disagree with its fundamental premises.) If you say that a socialist system is not an economic system or that home economics is not because it doesn't involve a pricing system, then you define them out of the category of things to be studied seriously.
I don't see much to fault Buechner's definition of economics. If I must, I would say it is too wordy. Compare it to George Reisman's definition: "economics is the science that studies the production of wealth under a system of division of labor." (CATOE 15b)
A definition in my view should only highlight the positive characteristics of the referents (if it is a positive concept). It should not bring in the abnormal, the fringe, the disputed. It should not zero in on the penguin at the expense of the pigeon in the everyday context. I would prefer understanding the core concept first before venturing to examine the peculiar cases.
In this light, Buechner's introduction for the reader is a good one.