I was in Mexico City several years ago and didn't see a whole lot of that, but I believe it as it's the 6th largest city on earth (in terms of population). I will however attest that the areas of Morelia, Acapulco, and the eastern side near Tulum, and Playa de Carmen all have ZERO homelessness as far as I could tell... I would attribute this more to the priority of family in Mexico over any governmental regulations though.
RE: Restaurante San Miguelito en Morelia, México - FULL TOUR & Comparison of the U.S. & México Food Industries / TOUR COMPLETO & Comparación de las industrias alimentarias de Estados Unidos y México (ENG/ESP)