Just to muddy things up more...

To me, wide, flat bars feel less maneuverable. Even though I don't consciously turn the bars with my hands, wide bars feel like they're pulling my hands around a wider arc, farther away from my body on the outside and tucking inwards on the inside.

I don't think that mountain bikes got wider bars for better leverage in turning the front to steer, I think that they provide better leverage to keep the wheel straight while it bangs against roots, rocks and ruts. Rotating a bike's handlebars doesn't take much effort at all, honestly; but when the terrain tries to knock it sideways, the extra leverage of a long bar is nice.

Like I said, though, I don't consciously steer with my hands, especially not on the road bike. When I'm going slow, such as transitioning from the street to the sidewalk in front of my building, I just look where I want to go and lead the bike there. If it gets rough, I don't grip any tighter, I just get out of the saddle and lightly hold the bars, making sure that the front mostly stays forward (just the same as on my flat bar bikes, actually).

To answer the original question, I'd say that it's just something that you'd get used to. I've seen chopped bars on fixed gear bikes used in bike polo, and they were barely as wide as my 15" laptop -- so those riders are obviously used to riding very short bars.