I would say 'Style'. remember, these are Italian, where style was born
Anyway, these are trully beautiful ships.
Precisely on all accounts.
For the most part all cruise ship funnels look like that underneath the almost purely cosmetic sheetwork most people are accustomed to (though particularly on Carnivale ships the "wing funnels" do serve a function, making sure exhaust gasses are properly vented over the deck so as not to compete with the onboard food and lack of sanitation to make people nauseous [zing!]). The latticework gives the same outline as the fairings over other cruise ships, but as to why a lattice and not a full fairing, I'm guessing it was an aesthetic choice to help set these ships apart (they're not the only cruise line to do this either).
P.S. Carnivale Cruise Lines suck