It's a lot more than a cute saying. Stanley Marcus, and his father before him, made it a way of doing business.
I'll explain why "quality"
can't be rationally defined, and why trying to do so will always be futile and deteriorate into navel-gazing. Get comfortable, because this might take a while (but you asked for it

).
First, let's do a little substitution: instead of saying that a certain product has quality, let's say instead that it's
beautiful. I, a random individual who's looking for a product, believe that this is a beautiful car:
I think it's beautiful because it's exactly what I'm looking for. I need parts, or I want to restore the car. Is this a "quality" car? It is to me.
Aside from the quality-in-the-eye-of-the-beholder idea, there's another impediment, and that is that "quality" is a
political word, here using "political" in its broadest sense, as in "company politics." For this I commend to your attention the 1946 essay by George Orwell entitled
Politics and the English Language which I've recommended before.
In the essay, Orwell says this of political language:
Except perhaps for the murder part, this is precisely what is done with the word "quality."
Orwell goes on to say:
(Bold added)
So you see, "quality" is rendered meaningless not only because it exists in the minds of individuals--and their own definitions might not be in concert with one another--but because businesses use it as political language in the same sense that Orwell describes the use of "freedom" and "democracy." They are like Lewis Carroll's Humpty-Dumpty in
Through the Looking Glass, who tells the incredulous Alice that words mean precisely what he intends them to mean, and nothing more (and nothing else.)
So while others try to put toothpaste back in the tube in attempting to a compose a one-size-fits all definition of "quality," I'll side with Mr. Marcus. Find out how to make money by making customers want more of what you're selling, and don't get eaten by a carnivorous amphibious reptile while trying to decide whether if it's an alligator or a crocodile.
That's all I have to say about that.