Dammit Jim, pick some damn rules and stick to them. Constraints make good drama. I doesn't count if the plot can be resolved at any time by some idiot in a Jefferies tube.
I used to hold up Star Wars as an example of good consistency. Then Ep. 1 came out. My wife asked me (5 minutes into the damn movie) why the Jedi bothered to swing their light sabers at the robots if they could just wave their hands at all of them and knock them over in groups. Gah. I sensed a great disturbance, as if a thousand sharks surfaced and were suddenly jumped...
In non-geek genres, most people don't much notice inconsistencies, whether they're pedantic things like "someone goes the wrong way to get to his bedroom" or bigger things like, "When did this character become afraid of dogs? He had a Great Dane back in first season!"
ETA: Try trawling the TV Tropes wiki for eight zillion examples of how TV writers of contemporary sitcoms and dramas can't even be consistent with the real world the stories are set in. :)
There's plenty of movies full of huge technical flaws I could point out an enumerate in an instant during only the first run through. They jump out at me, I see they are there, but I ignore them. This is what Suspension of Disbelief is. The only time it breaks, at least for me, is when the flaw is so bad as to be comical, and so comical as to make me loose my composure.