The beverage packages are just an option, and actually Carnival has them too. All the mainstream cruise lines are offering them, and even some premium lines. People buy them because they think it is a better value than buying drinks one at a time. If you don't want a package you can always buy sodas, alcohol, specialty coffees by the drink.
The basic beverages for meals, juices, lemonade, etc., are covered in your RCI cruise fare, again, just like with Carnival.