I build the BreezeUAV project without radio system and now that the project become good enough to fly, I regret it.
Firstable XBee are great, but sometime the communication is lost and my failsafe capability is not good enough.
Secondly, it's always better to have two links of communication and be able to switch from one of them automatically.
In my project, I don't control the plane directly. A joystick is used to define the pitch roll yaw and speed, those data are send to the UAV which try to achieve that attitude and speed goals.
I'm updating data from ground station to UAV at 30 Hz, while telemetry from UAV to GS is download at 1 Hz. Using a radio, I'll be able to increase the telemetry data rate.
It feels good to build cheap system, but when they crash ... Safety is always better :)