Unreal 3 runs on my computer.....at 10 frames per second. Epic doesn't believe in video settings. They are like a restaurant that won't let you make subtractions/additions to your meal.
1. There's no Unreal 3, that series ended with Unreal 2. Do you mean Unreal Tournament 3?
2. Video settings are up to the developer of the actual game, the engine has TONS of tweaking ability and apparently people hack the ini files all the time. Many developers are exceedingly lazy when porting console games to the PC, in the worst cases you won't even get to change the key bindings and the game will prompt you to press XBox controller buttons. On the other hand games like Blacklight Retribution (PC exclusive) have screens full of buttons and sliders to tweak the graphics. The engine has a ton of options but it's up to the developer to build GUI hooks for them.