It probably felt that way to most because I'm betting people played it after they had already completely leveled up. Most the dlc's actually felt better and more tuned properly if you did them low level. I really enjoyed experimenting with the dlc and tried them all with an level 1 character. Usually the hardest part of that was getting to the dlc area without gaining any xp and without dying. Going in to any dlc at level 1 with absolutely no gear makes them all so much more enjoyable. At any level, it was always more interesting to go in with no gear. I think the only one I had a lot of trouble with was NV's Lonesome Road.. Usually the dlc's still scaled to your level but dealing with those sentry bots in the beginning is pretty impossible. The dlc's that played best from level 1 were Mothership Zeta, Operation: Anchorage, Dead Money and Old world Blues.
The funny thing about the Fallout Dlc's.. If you did manage to start the ones you could at level 1, you'd come out of them around levels 15-20 depending on the dlc. I found it weird that both Beth and Obsidian had the same trouble of giving out too much xp for the level caps they themselves had implemented.