The Paris limits really don't compare with other cities of that size, the urban structure in France is completly different. Paris is like Inner London, not greater London. There's 3 times more "cities" in Paris region than in the UK. The concept is just completly different. Look at this link :
http://www.demographia.com/db-lonlanypar.htm
I think to reflect reality, the Paris diagram should be based on the core they define there, which consists in Paris and the "1st crown". Some people can pretend city limits are better comparison, but it's just hypocrisy and oyu know it, it's obvious it doesn't reflect reality, and that won't help the diagram to be easier to understand (like it didn't help Emporis, as if people curious about Paris skyscrapers would look in Puteaux, Courbevoie, or Nanterre...).
That debate is old anyway, but it's still stupid.