Here is a google map showing where is located La Défense. The district is mainly located on Puteaux and Courbevoie, but also extends to Nanterre. As you can see there are various municipalities which are totally independent from the development of the business district. That's why Emporis and Skyscraperpage, in considering municipalities as the thing determining all, aren't adapted to the Parisian case.
The Société Générale twin towers are themselves located half on Puteaux and half on Nanterre...