The research behind this claim may be a bit suspect (it involves someone named Dr. Beach from Florida International University, so perhaps a bit of state favoritism at work). But still, the list includes beaches from Hawaii to Cape Cod, so there is at least an attempt at inclusion. And if consistency matters at all, Siesta Key Beach has been in the top 10 several times in the past.
But I have something better than Dr. Beach. I have personal experience. And I can verify that this is a great beach, broad and balmy, palm-tree-fringed and full of the softest, whitest sand my toes have ever dug into. The natives call it "sugar sand." And who am I to argue. No wonder this place is so sweet.