You guys keep giving The Book precedence over actual physical reality. Kind of reminds me of another book and other groups of clearly similarly minded people... Where in the book does it say that Narziß himself is going to be paying for the associated (considerable) costs? 'cause a brewery is a business and like in any other business the bottom line is what really matters.
BTW is the English translation your own or is it from the official English edition? I ask because the translation for "in Hinblick auf eine sauerstofffreie Würzebereitung" is strangely missing completely. A fact that, curiously enough, makes the statement take on an absolute value which it does not have in the original text. The missing part translates to "in order to achieve an oxygen-free wort processing". So what Narziß is really saying is "If and only if you require an oxygen-free processing then the use of degassed water is absolutely necessary both for mashing as well as for sparging". The statement points to the fact that untreated water inevitably contains large amounts of oxygen, so that the use of untreated water would render any other measure such as the use of a Vormaischer or the flooding of all vessels and pipes with inert gas rather pointless. To paraphrase, it would be akin to setting up a new burglar alarm when burglars have already emptied the house of all valuables.
Besides all that, your claim that anything you read in Kunze MUST be fully implemented in ANY German brewery is utterly ridiculous. That's a University level text, covering the subject as broadly as possible since it is supposed to support an equally broad education. In Kunze you'll even find practices that are strictly "verboten" in Germany like the use of unmalted adjuncts or forced carbonation and much more. Would you like to claim that German breweries are implementing those illegal (at least for them) practices because The Book says so or would you rather just choose at will the parts that only suit your agenda and support your unrealistic claims? Shall I go on?