Extra Time with Bob Costas and Al Michaels (HBO) Bob Costas is stepping down from hosting the Olympics on NBC and Mike Tirico will replace him. USA TODAY SportsCostas took over the Olympics prime-time hosting role in Barcelona in 1992.(Photo: Ron Chenoy, USA TODAY Sports)For a generation, Bob Costas has been the face and the voice of the Olympic Games in the United States, a principled, steady and versatile presence...