All of the affiliate stations subscribe to a wire service and they all share the days news. The big services are the Associated Press, (AP), United Press International, (UPI), and Reuters. There are also specialty services foe business and weather. News gathering is fed to the wire services and then distributed to the stations. So, as your local affiliate goes to air, they have picked up the stories from the services and that's what you get. Homogenized news at it's best!
The local news is generally gathered locally if the station is large enough, or they get the local news from other stations for a price. But the number of people in the field gathering news is getting smaller, and the demand for TV and the Internet is becoming larger. The trend? Less real news and a lot more opinion from pundits with an agenda. Someone at these wire services decides what will sell and the decisions are questionable. For example, we have been in Libya for three months, Kadafi is still in power, and we hear nothing. Did you hear about the baby ducks...