What happened to tv series... ?

There was a time when a tv company showed a series in, say ten parts.  Every week on the same day and time your favorite show would be on.  Remember the old Batman series ending "Same Time same channel next week" it meant you could watch your series without trying to figure out when it was on. Common sense you would say.
Well not to the Americans it seems, try watching most US series and you'll end up either searching through the tv papers, or worse missing your favorite show.
Take the Big bang theory for example, they've had something like 3 episodes since before Christmas, and we're well into February, even worse the days and time change, that coupled with the constant showing of untitled repeats means the chances of actually seeing or recording the new episode is slim.
Criminal minds has stopped for the second time since Christmas, why the breaks? 
Once people start missing new episodes they tend to give up watching, you soon loose the thread of the story, or you tune in and find someones died and you have no idea whats happened.
I really can't see any good reason for mucking about with the viewers, it's the viewing figures that are key to keeping a program running and bringing in advertising revenue.