You know, it's kind of weird because you get people arguing from both sides, generally disparagingly about the other position and equally passionate that the have the right answer.
On one side, there are people who say this is all marketing hype with no substance and so you shouldn't buy a superfruit product (http://www.nutraingredients-usa.com/news/ng.asp?n=71664-cspi-ftc-super-fruits). If you do some digging you will find that most superfruits have at least some science support, and for the most well known like cranberry or pomegranate very solid scientific support of specific health benefits.
On the other side, some try to define something as a superfruit because it has a high antioxidant level or some other type of science support. This position ignores the fact that lots of fruit have high levels of antioxidants, but they are not all superfruits.
My position combines both of these positions - you have to have science, but more than that you have to have very effective marketing and if I had to choose, I would choose marketing over science. Marketing will get you science (by making sales you can fund science) but science by itself will never be enough.