It's to let us know it's not made with high fructose corn syrup, which is much, much worse than sugar. The corn lobby is trying to make it illegal for products to advertise that they use real sugar, and since the FDA is owned by Big Pharma and Big Agriculture, it will probably come down the pike soon. Do some research on high fructose corn syrup, and you'll see why this is nothing to laugh about. HFCS is in nearly everything, sometimes called "corn syrup," sometimes "corn solids," and even "corn sugar". Avoid it like the plague, if you value your health.
Even beet sugar is from genetically-modified beets, which is also bad. Best to opt for pure cane sugar, if you possibly can. There are much better reasons to avoid carbonated drinks than sugar, by the way.