Actually, cheaters do win from time to time, but not in today's Supreme Court decision in Shaw.  The Heritage Foundation summarizes the Court's unanimous opinion, per Justice Breyer, as follows:

Federal law makes it a crime to defraud a bank. Shaw obtained a customer's bank account numbers and used them to transfer funds from the customer's account to his. Convicted of bank fraud, Shaw argued that the statute makes it a crime only to "defraud a financial institution," not one of its customers. In a unanimous opinion by Breyer, the Supreme Court upheld Shaw's conviction. The Court stated that either the bank deposits are the property of the bank as well as the customer (which is why the bank can earn interest on the funds) or the bank is the custodian of the funds for the customer (which gives the bank a possessory interest in them against everyone except the customer). That neither the customer nor the bank suffered any financial loss is immaterial, because the statute does not require any such proof. Cheating a person or a bank out of insured funds is still fraud. Nor does it matter that Shaw had no purpose to defraud the bank, since the statute requires only that he had knowledge of the fraudulent scheme, which he clearly had. Finally, the statutory text is clear so the Rule of Lenity does not apply.