OB,
It comes down to simply being honest. If you bring an electronic item down for your personal use, customs expects you to take it back with you. If you do not take it back with you, this is not what is keeping with the "personal use" concept (please dont confuse this with something that you can "use up" like soap, shampoo, etc). So yes, if you fail to bring back an electronic item that was declared as "personal use", whether you want to believe it or not, you are breaking the law.
Jamaica is NOT the only country that does this. There are restrictions in the US and Canada as well for items that come in the respective countries. There is nothing comical about it - the rules are set up to protect each country's economy.