From PS3 Attitude: "Before the idea of downloadable content was around everything was included on the disk, cartridge, or whatever media the game was on. If a feature was not immediately available, then it could be unlocked by progressing through the game. Players were rewarded for meeting requirements such as beating the game or finding all the collectables, lending itself to greater replayability.
Now that everything is connected to the internet we are able to extend that playtime even further through downloadable content. DLC can take the form of anything from extra chapters that expand the story to new characters. But when do we draw the line on what DLC is worth? What price are gamers willing to pay to get that extra content?"