There are a couple reasons:

- Bigger Screen compared to a smaller screen on the DX3S
- 30 Model Memory compared to 10 Model Memory
- Faster Responce Time
- 3 Position 3rd Channel compared to only a 2 Position 3rd Channel
- And true DSM2


Yes the DX3S can now use the DSM2 receivers. The DX3S actually always used DSM2, but one controls the telemetry and the other the actual car receiver. The upgrade now make is possible for it to be used with true DSM2 receivers, but it is not as good still as the DX3R's DSM2 because the DX3S still needs to use it for telemetry. With a 3 Position 3rd Channel you can do things such as DIG control on crawlers. Bascially instead of only doing two thing with a third channel you can do three different things on the DX3R.

Both are good radios and for the everyday basher to the average racer the DX3S will be fine. But for the more serious racer or a person needing a three positon third channel the DX3R would be the better choice. Sorry if this is hard to read I am typing it on my iPhone.