Through two exhibition games, the 49ers' defense has been outstanding.Both the starting unit and the backups have yet to give up a touchdown in games against the Broncos and Chiefs."A lot of guys are stepping up and making plays," linebacker Aldon Smith told Cam Inman of the Bay Area News Group after Friday night's 15-13 victory over Kansas City.While it's hard to read too much into exhibition-game performance, the 49ers defense has been given a transfusion of young and veteran talent.The return of linebacker Parys Haralson, the emergence of nose tackle Ian Williams and the play of rookie safety Eric Reid and veteran cornerback Nnamdi Asomugha all have contributed. Then, there's Glenn Dorsey.The former Chiefs first-round pick returned to Kansas City for last week's exhibition game and continued his solid play this summer in his new uniform.Dorsey is listed behind Williams on the defensive depth chart, but he's been used in a variety of spots along the defensive front. Against the Chiefs, Dorsey and other members of the front seven put constant pressure on K.C. quarterbacks, sacking them seven times while also allowing just 72 rushing yards.For Dorsey – who admitted to...