The reason why there's no shadows for objects in the game is because Obsidian didn't really enhance the graphics at all. Now, I'm mostly fine with the graphics in Fallout 3, they're not really impressive compared to newer games, of course, but for the most part, I can accept them, though some of the textures could do with improving, but that's something modders can fix easily enough, however, I wouldn't have objected if shadows for statics were added into the game, mods can't do that so easily, but obviously, Obsidian decided not to do that, which seems kind of like a pointless decision in retrospect, seeing as the game was still buggy, you'd think that if they didn't bother updating the engine at all, they could have made the game more stable, seeing as they were working with technology already tried with Fallout 3, their programmers could focus more on polishing the game's coding since they didn't have to spend time on updating the engine, maybe that would even have happened if this game were made by a different company, but evidently, the qualifications programmer's and testers need to meet to be hired at Obsidian are the same as for Bethesda, which judging from the stability of their games I'd guess are pretty low, add that the game is running on an engine programmed by Bethesda, I guess hoping for a game that wouldn't have lots of bugs would have been pretty foolish. In fact, maybe that's why they couldn't do shadows, maybe on a better programmed engine, dynamic shadows for statics could have been done on consoles, but the current engine is just not that good.
Though personally, I'd say it's about time they entirely abandoned the Gamebryo engine, it's an old engine already, and their attempts to use it have been consistently buggy. Sure, they can update it, it's pretty clear that they updated it somewhat from Oblivion to Fallout 3, but eventually, there comes a time when you just have to abandon old technologies in favor of something newer, I would say that time has come with the current engine, maybe in the next game...
Shadows are very resource intensive, particularly with the amount of clutter in the game. While this might not be a problem for most newer gaming computers the engine has to work on the XBox 360 and PS3 as well.
And yet in the recent games I've played on the Xbox 360, there has always been dynamic shadows for things other than characters. Besides, they could always allow players to activate full dynamic shadows as an option on the PC version but have it not active on the console versions, but I guess they can't do that, after all, that requires actually doing something for the PC version that's not in the console version...
Or if shadows for clutter would ruin the performance on the console versions, maybe they could just do them for environment objects like buildings, trees, rocks and such, because while I can usually ignore a coffee mug not casting a shadow, standing in the shade of a building yet not actually finding any shade at all kind of hurts the atmosphere of the game, really, I'd actually say these things should get priority BEFORE characters when it comes to casting shadows, yet in Oblivion, Fallout 3, and New Vegas, characters are the only things that cast shadows.