I do not believe there is any difference. Having said that, I would say that edible is far more commonly used, at least in AE.
Having said that, I would also say that I might use "eatable" if I had cooked a meal and was saying to my guests that I hope it is "eatable," that is, palatable. Saying it is "edible" might tend to mean that it is technically capable of being digested -- grass is edible to a cow but not to a person, for example.
However, I still say that they can be used interchangeably.