I see much information written in this and other forums regarding passports that is simply incorrect. To clarify. If you do not live in Italy and your passport was issued by a consulate in the USA, for example, you do not have to renew your stamp every year, whether or not you have been to Italy. If you bought a round-trip ticket in the USA with your American passport, you can depart Italy with your American passport as long as you're not an Italian resident.
And there are even exceptions for Italians who do live in Italy regarding this stamp. I recently returned from a cruise on the Italian cruise line, Costa. At embarkation in Italy, I presented my documents (Carta d'Identita and Italian passport) to Italian authorities and even though this cruise was stopping at ports of entry which were not in the European Union, nothing was mentioned about the stamp in my passport last renewed in 2009. I'm sure many of the mostly Italian passengers also had expired stamps but we all went ashore at ports outside of the European Union with no problems whatsoever.