Futaba compatibility has been excellent. My old FF3 (c. 199-something) was compatible with every Futaba servo and receiver ever made until the 3VC, and with the Spektrum 2.4 when it first came out. Most other racers were buying new radio to use 2.4, whereas my FF3 just plugged in and worked - in a 15-year-old radio!
Things have to move on, so it is the 4-series radios that have moved things on again. I reckon that two upgrades, with lack of backward compatibility, in something over 20 years is not a bad record.
I appreciate the point, but I don't think Futaba are losing out. The 613 and 614 receivers are small enough for a 12th car, and they don't come much more space-challenged than that!
Air/surface systems differ because the requirements for meeting US and EU standards for air control are far more stringent than surface control. Additionally, weight is a major issue for aircraft, especially now that electric flying with LiPo is such a growing class - weight is a selling point for flyers. Add to that the much lower need for power to servos and speedos in most aircraft, and you can make something very small and light for a 'plane that wouldn't work in a car or a boat. HTH
