Something happened on the way to the 2008-09 television season: Viewers decided they had better things to do. Television network viewership is down overall, and some higher-profile genre shows like “Heroes” on NBC and “Terminator: The Sarah Connor Chronicles” on Fox, are really starting to feel the pinch. “Heroes” slid to a 5.7 rating/8 share, according to Fast National ratings from Nielsen Media Research. That was down more than 3 percent from the 5.9 average the show received in its two-hour premiere, and is pushing the bottom of its ratings lower and lower each week. While it was nearly 43 percent more than its lead-in of “Chuck,” “Heroes” finished behind comedies on CBS as well as reality television on ABC. While ratings for “Heroes” might be slipping, it’s not nearly as bad …