Why are the front rotors so much more substantial in design than the rear? It seems that it would make sense to have all rotors be the same. The thin rotors just seem so puny....thanks for the replies.
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75% of braking power goes to the front due to the weight transfer when you're stopping. It's controlled by something called a proportioning valve. The rear tires really don't have much stopping power due to the weight transfer. Since they don't have stopping power, it doesn't make sense to hang heavy brake gear off the rear. SInce the front has to do most of the work, i.e. convert kinetic energy to heat, they have to be beefed up to handle it.

 

If you ever ride a motorcycle in your life (driver or passenger) you'll rapidly find out that you sqease really hard the front brake and barely touch the rear one!!

That's why there's two disk in front and only one in the rear end!!

Same principle apply to car!!