According to the Wall Street Journal which quotes sources in Cupertino, Steve Jobs keeps a close eye on his company in spite of the fact that he announced to have taken a break. Even though he leaves the current management of the business with Tim Cook, he is never very far away and continuous to supervise the important projects and the testing of the future products. He would thus devote time to check that the iPhone OS 3.0 interface matches his expectations.
In addition to the fact that this advertisement comes at good time to please the markets, it reassures us on his health condition, something that we have no information on since he announced his temporary withdrawal.