The Millionaire Next Door is not a great book - it's just survivorship bias and assumes correlation is causation.

http://www.latimes.com/business/hiltzik/la-fi-mh-the-death-o...

Plus one of the authors died driving a Corvette, not a Corolla...

Like all self help books, it's about selling hope.

Furthermore, you were entirely unwarranted in making the assumption that the GP has a spending problem instead of an income problem.