Keep in mind that "Italy" was not officially a country until the mid 1800's. That is why the people in Milano and Torino look and speak differently than people in Napoli. Presently there is a move on for these northern areas to secede from Italy because their industrial wealth subzidizes the South.

Sicily, as someone noted was invaded over and over by the Spanish, the Arabs, and even the Normans, and because it is an island the people there took on characteristics distinct from those on the mainland. Even their dialect is different. The most pronounced difference is that vowels at the end of works gets dropped, hence "prosciutto" becomes "prozhut" and "mozzerella" becomes "mozzerell."