You know, that sounds very familiar, where have I heard that before...
O right, I did the exact same thing when I was younger. I wouldnt worry too much about it. Just explain to him that the commercials dont always tell the truth, and that he shouldn't trust everything they say. Also explain the concept of limited funds. I dont know how old he is, but your best bet would be to give him money instead of toys for his birthday/Christmas, and let him buy the toys and games he wants. That way he can learn first hand that he has limited funds, and that he should buy things that he will enjoy. If he winds up buying something from an infomercial with his birthday funds, and then finds it useless, then thats his problem. He could have had something else more useful instead, but was up to him.
Sometimes people learn best by making mistakes. Best to let him make mistakes and run out of money while he is still young.