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According to Eurogamer's Face-Off maestro Rich Leadbetter's blog, Inside Digital Foundry, the auto-update patch introduces specular maps to certain areas, delightfully illustrated with shots of bugs and a comparison video.
The Xbox 360 version was the better of the two console releases when Fallout 3 released in late October last year, but as Leadbetter points out, "despite its superior frame rate and full-on 4x MSAA, [it] had flaws of its own - notably some inferior textures when viewed close up, along with a lack of specular maps on the monsters and characters, resulting in a somewhat flat look compared to the other versions of the game".
Source: Eurogamer