Keeping that in mind, it's expensive to keep a show on the air for eight years -- escalator clauses in actors' contracts call for yearly salary increases, union crew members' expenses go up, etc.
Yep. This is why most shows that don't get cancelled tend to wrap up after 5 or 7 seasons, and why most of the shows that run longer are ones with heavy cast turnover (for instance, Smallville
, beginning its 9th season tonight, has only two of its original leads remaining). This is why Power Rangers
changes its entire cast on an annual basis.