The single crank steering used to be optional until the 09 car came out then it was installed as the default steering system. All previous E4 cars had the dual crank system. The E4FS, E4RS and the 09 RS can have either system installed. TM introduced the E4 then updated to both the E4FS and E4RS to make the car more specific to either foam or rubber tires. The 09 E4RS just further refined and updated the E4RS to accept brushless motors and LiPo batteries better. The Plastic fantastic was introduced around the same time as the 09 car. Now TM seems to be focusing on drifting options for the car.
I don't get the whole drifting thing but to each his own.