It's had an actual flame retardant chemical in it, and still does. The ingredient is called brominated vegetable oil (BVO), and its been patented in Europe as a flame retardant

A spokesperson for Gatorade's owner PepsiCo, Molly Carter, mentioned to reporters that Pepsi had been considering removing BVO for about a year, pending their discovery of a new and better replacement ingredient that wouldn't alter the taste. Molly claims the petition from change.org with over 200,000 signatures had little impact.

Ah yes, you can hear Gatorade consumers concerns: "Yum - this fire retardant sure is tasty. Wonder if I can get some pure BVO if they take it out?"