The level, stat and skill caps you have in Fallout 3 - 30, 10 and 100, respectively - seem to be hard numbers that Bethesda Softworks isn't inclined to raise further.
MTV Multiplayer recently asked Bethesda Softworks' Jeff Gardiner if there were any plans to extend the game's level cap, as was done when Broken Steel took it from 20 to 30. Gardiner was also asked if the game could handle boosting the stats above 10 and/or the skills above 100 without breaking. Short answer, no.
"I know from the outside this seems like a fairly simple proposition, but doing this could unbalance the game in a variety of ways," he told Multiplayer. The game's replay value, he said, is in going through it again as different characters having different experiences.
Gardiner's followup didn't explicitly slam the door on a cap extension later. "We're very happy that people enjoy Fallout 3 so much that they want to keep playing it, and I'm sure we'll look into addressing these concerns in future games," he said.
We've heard never-say-never from Bethesda before, and it's a sound policy. But it sounds like "future games," means "games other than Fallout 3."
Kotaku AU Note: My own experience suggests he's right. It's already far too easy even on the Hardcore difficulty setting. Unleashing a level-40 character on the wasteland would totally break the experience, unless Bethesda rebalanced the entire game. Which ain't gonna happen.
Bethesda: Further Level Cap Increases Could Unbalance Fallout 3 [MTV Multiplayer via Joystiq]