All cars comes with a differential if not you would'nt be able
to steer the car if both the driving wheels are running at the same
speed.
The difference is that normal cars comes with a open gear type
differential. For performance cars, it either comes with a Limited
Slip Differential (LSD), Torque Sensing (Torsen) Differential &
Electronic Differential. Some rally cars uses a Active Torque
Biased (ATB) differential, which is available as a aftermarket
product for certain performance cars.
Traction control is a type of electronic differential system
where the power transmission to the affected wheel is cut off when
the traction sensor senses the wheel lost traction with the road.
The sensor works when the wheel goes at unusually high rpm as
compared to the other driving wheel. Power is regained once the
wheel regains traction with the road.
Aftermarket differential such as performance LSD or Carbon LSD
are only available for performance cars such as WRX, Evo or Mazda
RX8. ATB Differential are used more for continental performance
cars such as BMW M3 because the only company which manufactures it
is in UK.