They came out wtih FASST first. It appeared to be targeted more to the high end customers that are Futaba's biggest buyers. Solid as a rock but quite expensive.
Meanwhile Spektrum was cleaning up in the entry level and beginner market, the market of the future. As Spektrum has advanced their technology they have done a superb job of maintaining backward compatability.
Apparently Futaba they could not bring down the price of FASST so they released FHSS, more focused on the lower end and entry level market. As Kyle stated, they will start coming out with radios that can do both, or all three.