That is correct. The only commercially-available combat module that I have ever seen is ParkZone's for the Firebird/Aerobird series of RTF planes. It's not compatible with "regular" radio systems.

Frankly, I have yet to see one in action. Regular streamer combat is only a fringe activity (unfortunately). The ParkZone combat module would have to be a whole lot more popular to give companies a profit motive to come up with one for regular planes.