Luchaire's mod fixes this, and randomly assigns height values to any NPC you encounter. The backgrounds, like the game introduction sequence.
The loading screens show snippets of the general information that is found in the stats section under the general tab on the player character's Pip-Boy 3000, along with information regarding the various perks, creatures, factions, people, and locations of the game. The default version of FO3 features hundreds of NPCs, all of whom are somehow exactly the same height. This page is a list of loading screen hints and slides found in Fallout 3.
This mod fixes that and helps the game run on newer hardware. The default version of FO3 isn't optimized for Windows 7 or above, meaning that it isn't utilizing all the memory that a 64-bit OS allows for. This mod by SkyRanger-1 helps the game avoid all those troublesome crashes and framerate stutters during gameplay.
This is a must-have, even if you don't plan to install any other mods. In what might be the most important mod for Fallout 3, creators Ben Wah, Hairylegs and prisoner416 have managed to fix and patch almost every bug that the original retail version of FO3 suffered from. While there are dozens of mods that improve on or add new content to Fallout 3, there are also a bunch that update and improve the core mechanics of the game itself.