Well I'm at the disadvantage of having not played them, but just looking at number of quests and number of locations...
Broken Steel: 9 total quests, 14 new locations (added bonus of raising level cap).
The Pitt: 6 total quests, 16 new locations
Point Lookout: 11 total quests, 44 new locations
Tribunal: 38 total quests, 25 new listed locations
Bloodmoon: 44 total quests, 65 new listed locations
Shivering Isles: 39 total quests, 56 new locations
Of course, quests and locations aren't the end-all-be-all of what makes something worthwhile, but still...
If they want to make expansions and call them DLC, that's fine, and if that's what things like The Pitt, Broken Steel, and Point Lookout are, ok. But something tells me those three are not exactly what I think of when I hear 'comparable to an expansion.'