The times are changing in the TV news business. With Diane Sawyer replacing Charles Gibson, who is retiring from ABC at the end of the year, women will anchor two of the three major network evening newscasts. Katie Couric, who became “CBS Evening News” anchor in September 2006, was the first woman to hold the job that made icons of Walter Cronkite, Huntley and Dan Rather. Brian Williams at NBC is now the minority.