You mean, expansion packs which have just as much content as they normally would, just like any strategy game since C&C has done?
http://en.wikipedia.org/wiki/Civilization_IV:_Warlords
Warlords added many new features to the original game. These include:
A new category of Great People known as Great Generals;
The ability to institute vassal states;
Eight new scenarios[2]
Six new civilizations playable in single-player and multiplayer;
Ten new leaders (including new leaders for existing civilizations);
Three new leader traits (Charismatic, Protective and Imperialistic);
Unique buildings for each civilization;
Three new wonders;
New units, resources, and improvements;
Core gameplay tweaks and additions;
Inclusion of all patches released for original Civilization IV.
http://en.wikipedia.org/wiki/Civilization_IV:_Beyond_the_Sword
New content includes:
10 new civilizations and leaders (Babylonia, Byzantine Empire, Ethiopian Empire, Holy Roman Empire, Khmer Empire, the Mayans, Native Americans, Netherlands, Portugal and Sumer)
6 new leaders for existing civilizations (Abe Lincoln, de Gaulle, Boudica, Darius I, Suleiman the Magnificent and Pericles).
25 new units, 18 buildings and new technologies added primarily to the late game.[16]
11 new scenarios.[5]
6 new Wonders of the World.
New diplomatic resolutions through the United Nations.
Then you had Civ4: Colonization which was a standalone remake of the original Colonization with the Civ4 engine.
So Civ4 did exactly what Blizzard plans to do: add unique civilizations and single-player scenarios to be played along with other general improvements.
The only difference between Blizzard and Firaxis is Blizzard is upfront about how they are going to split up single player content and have yet to divulge their pricing scheme.