It’s been a bad week for long-running TV shows. Yesterday the news broke that NBC had cancelled “Law and Order,” then today Deadline Hollywood announced that “Heroes” is getting the boot. The series fell victim to that familiar combo of low ratings and high production costs. Unlike the surprising demise of “L&O,” this cancellation had been rumored for some time. I just hope all those new shows NBC has waiting in the wings will be able to please more viewers than the old favorites they’ve dropped.