OP supresses the central nervous system. Non Steroidal Anti-inflamitory drugs (NSAID'S) such as ibeprofen or other pain relievers such as tylenol and asprin help take away pain. The OP however just mask it like in Hydrocodone which is a combination of OP and tylenol and I think pers are just straight OP but I'm not too sure. So if you notice a person who has has had surgery and is in alot of pain they normally don't get too much of a high compare to a person who has minimal pain and gets high off the same dose. So when there is WD from this OP the original pain is still there plus more pain that the OP has caused because now your body is asking for the drug and causing our body to have pain in order to get the OP. But it is very possible to get off these OP. It's not easy but the more you know what to expect the more you will be successful.
I dont know a direct answer to your question but I think it has everything to do with the pain receptors in our brains, everyone has a different amount therefore, it would take more or less for some people to get high. I am on percocets as well and have for about 3 years. How did you get addicted to them?