Chimera 1
Super Freak
I can't think of a FPS that they actually added an entire new campaign mode just so they didn't have to come out with a new game.
They are doing it for Gears 2. They are coming out with a new campaign chapter later this summer.
Fallout 3 got campaign add ons. Oblivion got Shivering Isles. Tomb Raider: Underworld is getting campaign add ons. Mass Effect etc...the list goes on. So yeah game companies are doing this.
The DLC is a ripoff without a doubt, but they also provide game patches and bug fixes for free. DLC worth it's salt will extend the life of a game and keep people playing it. Gone were the days when you had to wait for the sequel to get the patches and bug fixes.
So yeah i think they are asking a lot for people to drop another 60 and not supporting the first game.