A few freshmen shows (as ever) get canned after their first seasons, a few old favourites (or once favourites) are winding up after their years and years.
Every channel wants that magic gift, a hit with the audiences; maybe something that will give five seasons, get that magic 100 episodes and float off into syndication.
Networks and viewers are less tolerant than they once were - shows have less and less time to impress and make an impact before the axe might fall. Even a proven creator, writer or actor is no longer the advantage it once was (golden boy JJ Abrams 'Alcatraz' was cancelled after the first season).
The saddest of all - there is so little quality in British TV these days that what happens to American shows really does matter; at least in this house.