Good DLC: Content created after the game, like Dawnguard, Dragonborn, Shivering Isles, Knights of the Nine, Bloodmoon, Tribunal.
Bad DLC: Things that were, or should already have been in the game: Like Hearthfire and the infamous Horse Armour DLC.
Saying all DLC is cut content is retarded.
Certainly many and most DLC is crap, I mean look at Rome 2. However, it's stupid to put a blanket statement on something like that. There are so many games, so many developers.
You can't expect that all DLC, Expansions, and the like are cut content. I suppose it's probably worse with the smaller selection of games on consoles, but that doesn't make it true.