Aside from the tapes and Gravano, did they have anything or anyone else to testify against him? He went to the apartment because he knew the ravenite was bugged. Wouldn't common sense tell you to be a little more precautious. Like everything else with these guys, who knows what it's like to be in their shoes. Maybe he had a mole that told him that they had only the ravenite bugs giving Gotti a sense of security.