This article does a great job of explaining why I dislike the fact that TV shows and Movies are run almost strictly like a business, with no regard to the work that goes into creating the shows, and little regard of desires of the fans that watch them.
In short, I'd rather that things like cancellation decisions be reached before writers have no chance to finish their projects (who on earth thought that making decisions about cancellations should be done after a TV show's season has wrapped shooting?). At least with Joss Whedon's Angel they let him know about 4 or 5 episodes before cancellation, so he was able to wrap some things up in the storyline, but that is the only example I can think of. Otherwise, it's just the total luck of the dice whether or not your show will make it to complete your story lines. One option would be to move to a Japan or BBC-style system, where TV shows generally have a pre-arranged story arc (the only shows I can think of in US TV are Bablyon 5 and the BattleStar Galactica reboot) so that things aren't left open ended, and the executives know how long the show is supposed to last. With so many shows becoming more serial and less episodic, this would be one way of fixing the problem of canceling shows that are clearly going somewhere, and aren't just open-ended.
In short, making TV and films is about artistry on some level, and the fact that the studios and TV stations are run by businessmen means that the artistry takes a back seat to making money. After all, instead of letting some of these great movie writers and directors do their thing, let's make a movie based on Tonka Trucks!
I was talking with my father-in-law, an economist, and he made the observation that I always rant against these various shows being cancelled or movies being mishandled, while he assumes there were some very good economic reasons for those decisions. Surely, though, between letting artists run wild with enormous budgets and studio businessmen making decisions that curtail creativity, there's plenty of room to find ways to make money without treating movie making like a production assembly line. But we veer way too much towards the "businessmen making decisions that curtail creativity" model.
Well, at least someone finally let Joss Whedon off of his leash. Avengers is the #3 movie of all time.
Sidenote: The preview culture is also ruining movies. Turns out, when people don't pay attention to pre-arranged flop narratives, they actually enjoy good movies.