enigmaxg2: If people keeps buying DLC's, game developers will continue to split even more parts of the games to sell them separately.
I'm still waiting for a DLC which is worthy to be called expansion.
There are a few. Dragonborn and Shivering Isles are probably the best examples in my mind as both added to the main game without MISSING from the main game in their absence.
The Pitt in FO3 is pretty good too, though it's a little small for a full fledged expansion, it's also lower priced than most expansion packs were.
The Dishonored DLC and the Dark Souls and Dark Souls II DLC are also pretty expansive, with all 3 Dark Souls 2 costing just $25 (with the season pass) and being about half as long as the original game. The Abysswalker DLC for DS1 was pretty big as well, and was fairly inexpensive as an expansion; it had good value for its price. In fact, most Bethesda games have good DLC (if you ignore the Horse Armor for a minute, which may be WHY they have good DLC after getting called out on the failure).
EDIT: I'm aware that DS and DS2 were not Bethsoft games, but they were the best non-Beth games that came to mind.