With eight of the top 10 shows, NBC won its 15th consecutive week and found success with its decision to get a head start on the fall season. The debuts of "Ferris Bueller" and "Parenthood," two new comedies, made their way into the Top 10 (finishing sixth and seventh, respectively), A.C. Nielsen figures showed Tuesday. NBC was first with an average rating of 10.5, compared to 9.4 for ABC and 9.1 for CBS, with each rating point representing 921,000 households. In the week's most interesting matchup, NBC's repeat of "The Cosby Show" overpowered a Fox rerun of "The Simpsons" (No. 54) last Thursday. The full list of ratings is on F9.