The term "luxury" (and similar terms) connotes a high-quality product offered at a premium price - it's a position that every brand would like to occupy, and that many claim to occupy, to the extent that the word has lost its meaning.
Not only to brands at the bottom of the heap seek to elevate themselves by claiming luxury status, but brands that begin as luxury products have debased themselves to gain more customers. Many luxury automobiles have affordable product lines, and the names of boutique designers appear on clothing at department stores everywhere.
Luxury has become a commodity, an empty concept. The author's point in writing this book is to dust off the term, explore what it once meant an what it has come to mean, and to consider luxury as "a different and global way of understanding."
A bit on the authors: once has been an executive who has developed and maintained "some of the most famous and profitable luxury brands" and the other has been an academic and consultant of brand strategy. Both are Europeans, and feel that luxury is a fundamentally European concept, in the same way that mass marketing is an American one.
Their approach in this book is to consider the norms of principles of luxury goods, which are significantly different to mass-market ones, and to demonstrate that a "luxury strategy" still remains valid in the contemporary marketplace. Even so, some of the principles of luxury are applicable to premium brands, and products can transition into and out of the luxury space, so it may nonetheless be of interest.