Why don't cars have slipper clutches
 

like motorcycles? As you approach a a braking corner on a bike, you can bang down 2 or 3 gears without having to rev match and then just let out the clutch, even at high speed and not worry about locking up the rear or over-reving the engine.

So why don't performance cars have this?

I have indeed induced a rear wheel slide on a motorcycle with over aggresive down shiftiing. I'm not sure why you think a car is any different, both must be operated within the confines of the gear ratios and redline. One big difference between sport bikes and cars is that with the bike you typically have 11, 500 to 16,500 rpm to work with... as far as slipper clutches go, perhaps it's due to there hardware not being up to the task of handling the weight..

Maybe I wasn't clear. With a slipper clutch, you can go down several gears, let the clutch out and the rear will will not lock up and the motor will not over rev. Without a slipper clutch, you can lock up the rear and/or over rev.

A motorcycle clutch is typically multiplate and wet (oil) and a automobile clutch is typically a single plate and dry.

Also, the transmissions are different. A motorcyle transmission typically does not have syncho's, instead it is a sequential transmission, more like those used in serious automobile racing.

Hence, the clutch/transmission on a motorcyle and a car have very different characteristics.

Plus the actual loads that a motorcycle clutch has to deal with vs an automobile. 5-6 times the power, and god knows how much more weight....

An automobile slipper clutch has been patented since the 50s, but I guess no one has tried to develop it for cars. And with the advent of PDK and similar systems, it probably won't be deeloped in the future.

Agreed, the clutch design is very different, it's cheaper and easier to do it via computer & flappy paddles. Also, the demand for such a device on a street car would be miniscule.
Slipper Clutch - How it Works

This was the point I was trying to make. Race motorcycle transmission components are dealing with 250ish hp (at the upper end of the scale) pushing arounless than 800lbs of rider and machine. The dynamics are totally different from an auto.

the new KTM 1190 r has what they call a slipper clutch. check out the the demo vids on youtube