This is the only way to place this combination of compounds, some salts, some acids (most carbonated beverages have a pH around 2) without resorting to details about the actual system which is known as a "buffer". The presence of carbonic acid and its conjugate base benzoate is a system that prevents drastic (10-fold) changes in pH. The solution exchanges protons in a system that is fairly constant. However, one cannot put both benzoic acid and sodium benzoate on the label as that is not what the ingredients that actually went into making the carbonated beverage were.
What is most disturbing is not the nominal inaccuracy of stating "sodium benzoate" on the label. The most distressing thing is that benzoate itself in a low pH environment decomposes into carbon dioxide and benzene. Benzene is a known Class 1 carcinogen and prolonged exposure at ppm levels can lead to cancer of the blood (leukemia).