I think they cap fallout 3 so that it can hold true to the desperation vibe.
I kind of like how each character can only become great at 2-4 different skills which keeps the game experience focused and unique to each play through.
As much as I love Oblivion, it is kind of a double edge sword. I have no clue what my guy is any more cause I have been blazing through enemies leveling up everything and whoring the game until its so easy its boring. Granted that's after 200 hrs of game play with one character.
When I realized that Fallout3 does not scale and the game is Finite it actually scared me. I battle differently, I drink radiated toilet/fosset water, and I feel like im actually trying to survive. For me it is all adding up to be everything I loved about Oblivion, combined with everything I didn't fixed.
and you can always just go back and play more oblivion