Just looking at the site from the link provided above I noticed some information that is no longer correct.
In the part on the page that says,"DO YOU PAY THE DIFFERENCE IN PRICE FOR BEVERAGE NOT INCLUDED IN YOUR PACKAGE".
Buying a beverage above the price of your package means you’re paying the full amount of the beverage. Unlike some cruise lines (NCL mainly) where you would just pay the difference, that’s not the case with MSC. So if you think you’ll appreciate the beverages that are not included in your drink package, upgrading is probably the best idea and it’s encouraged once you board the ship. This especially makes sense if you were given a promo Easy Package as part of your booking!
That has changed. Now you only pay the difference in price. On Meraviglia 2 weeks ago I had a couple purple rain drinks which are $13.00 and was only charged $3.00 each time.