If you have the DLCs, Three Dog on the radio will refer to taking back the Jefferson Memorial from the Enclave, even if it hasn't happened yet.
If you kill Mr. Tenpenny, the tower residents will continue to refer to him as if he were still alive.
Victoria will continue to harangue you to deliver the android component to Zimmer, even if Zimmer is dead.
The 50-star U.S. flag can be seen in-game on the Delta IX spaceship and a recruiting poster, when that flag never existed in the Fallout universe.
General Chase has a goatee, which is forbidden under U.S. Army grooming regulations.
General Chase makes reference to his rank insignia's gold stars. The rank insignia of a U.S. Army general consists of silver stars, not golden ones.
In Point Lookout, the naval recruiting center sign is misspelled as "Recruting".
One of the key aspects of Fallout 3 is that you can be encumbered at lower levels and carry a limited amount of inventory. Yet, when you shoot any of the gun's, as your ammo drops, so should your ability to be encumbered,.as ammo would realistically take up space,.so each time you shoot, your numbers should go down. Yes, ammo doesn't take up space in your inventory in game, but it would in reality and should have been counted in your inventory and should have brought your numbers down.
5.56mm ammo is misspelled as "556mm" in the Pip-Boy.
The whole concept of Fallout 3 is that it takes days and possibly years to complete the story line. Yet, there is no romance options available to you. There is some implied possible romances, but you can't romance any of the other characters. This would be impossible, as it's supposed to be open world and romances would occur in that amount of time. This game was made before romance options were more common, but there should have still been a option to do so. It makes no sense that there isn't.
In Mothership Zeta, Paulson is from the mid-19th century but he is equipped with a Smith & Wesson Model 29 handgun, which was invented in the mid-20th century.
Lincoln's repeater is shown as being chambered in .44 Magnum, but that cartridge wasn't invented until the mid-20th century.
The Dirty Water bottle is made from plastic but when picking it up it makes the sound of a glass bottle.
In the return to Vault 101 quest, the Overseer refers to your character as a man, even if it is a female.
In the game, you can see the Washington Monument from Germantown, Maryland. This would be impossible in real life, since the two locales are more than 26.5 miles away from each other.
Olney is portrayed as being far north of Germantown, when it's actually slightly to the south of it in real life.
One of the Maryland power stations is located on the Virginian side of the Potomac River.
Raven Rock is portrayed as being much further south than it is in reality.
One of the key aspects of Fallout 3 is that you can choose to be good, evil, or neutral. Yet, you can do things like terrorize Tenpenny Tower and destroy towns. Yet, if you attack Tenpenny Tower, everyone tries to run away from you, instead of standing up to you, and using there weapons, that they clearly have, as they are seen selling to you and trading with you. You can even leave Tenpenny Tower and come back, and they will act like nothing happened. Everyone will just hide from you in fear, and do nothing. They would have likely stood up to you, and likely used there weapons to kill your character. You should have also been banned from entering Tenpenny Tower again, as you committed multiple crimes, and would have likely been unable to return.
At the National Archives, Protectron Button makes reference to a "Royal Army"; however the British army is simply called the British Army.
One of the Brotherhood Outcasts mispronounces 5.56mm ammo as "Five fifty-six"; it's supposed to be pronounced "Five-five-six".
When a nearby male NPC dies when you're travelling with a companion, your companion will always refer to them as a female.