I do recall reading that there was some belief put to Smallville may have weakened the film because of people going by the same reason Berman had TNG cancelled after season seven: why would people go see it if they can watch it from home for free?
What???? Ending TNG was Paramount's decision because it got costlier to produce each season. Ending one show and starting another let them make new, more profitable deals, and a new cast meant smaller salaries. Actors get raises every season, so the longer a show stays on, the costlier it gets. That's why very few shows go beyond seven seasons, and those that do almost always have heavy cast turnaround (including Smallville
, which has only two original cast members remaining).