A Jew is not punished without 2 witnesses. A idol worshippers can be punished on his own confession.
A Jew may not be punished without warning, for he is only punished for a purposeful act. A idol worshippers, since he is punished even for something he does by negligence, may be punished without warning.
A idol worshippers has only one type of punishment, the death penalty. A Jew has many types, among them death, Malkos, Korban and sometimes nothing - although he will bear his sin as one who transgressed the King's commandment.