to me there are several reasons:
With the R you can do some serious off road ( and is fantastic on road as well)
The frame is better
The suspensions are superior
The motor is uncomparable, the GS might be better berween 1000 and 2000 rev, but for the rest forget it
Ktm is lighter
The way the traction control activates is way better on ktm
The look is better, to me the GS looks like mazinga Z
I don't like the rigidity of the shaft drive and I broke 2 in the past, no more!
Do you think it's enough??