In the days of 27mhz, 35mhz and 40mhz certain bands were allocated to different areas of the hobby as a means of segregating bands for the sake of safety of operating mainly aircraft. Nowadays with 2.4ghz sets there is no interference between sets so no need to segregate anything. Consequently 2.4ghz sets can be used for cars, trucks, boats, aircraft or anything else you fancy.
I have a Spektrum dx6e set and use the same transmitter to operate boats, aircraft, vehicles and even a steam lorry.