I think it may appeal to those that want to lower their sugar/carb intake, but are not trying to lose weright or anything.

I have an uncle that has always made his own 80/20 soda, as he calls it. 80% diet Coke, and then 20% regular, just to kill the diet taste. He isn't trying to lose weight, but he is trying to cut out a little sugar (he's a soda junkie) but still keep some of the taste.