The reason behind choosing a RC 2.4g TX/RX system over the Lego PF IR system is the natural of the model.
While Lego PF IR system is good for controlling multiple actions, the IR system has its limitation such as range and require line of sight. It is great for models with many different actions such as 8043 or 42009, but most likely you are controlling the model in a rather short range.
For this monster truck, I see the potential of this model that it will be great to be played in the field. The RC 2.4g Transmitter provide much larger range, for example, the Transmitter I am using have a range of 1km, and radio signal require no line of sight, which is more stable in controlling distance model.
Fitting massive lego motors into the small chassis is fun, but fitting RC parts into Lego model is also challenging. So why make the boundary to limited the possibility of this great model?
I will bring it out to the field and take some video later on.