Cheating and the rule of law

Here is the definition of cheating in the criminal code of Singapore.

Cheating – Whoever, by deceiving any person, fraudulently or dishonestly induces the person so deceived to deliver any property to any person, or to consent that any person shall retain any property, or intentionally induces the person so deceived to do or omit to do anything which he or she would not do or omit if he or she were not so deceived, and which act or omission causes or is likely to cause damage or harm to that person in body, mind, reputation or property, is said to "cheat". For example, A cheats if he intentionally deceives Z into a belief that A means to repay any money that Z may lend to him when A does not intend to repay it, and thereby dishonestly induces Z to lend him money. Cheating is punished with imprisonment of up to one year, or a fine, or both.

A Singapore lawyer told me that the attorney general will only prosecute cheating when it is in the public interest. So, if a citizen is cheated and lodge a complaint, the attorney general may not take up the case.

My friend told me that in America, the attorney general will look out for cheating cases and prosecute the culprits. They do not wait for a complaint to be lodged.

It seems that the system is different between Singapore and America. I am not sure what is meant by "the rule of law", when the law is only enforced at the discretion of the authority.