Irode my Serotta with the early '90s STI 50 miles yesterday with this conversation in mind. When I'm riding the hoods, my hands are firmly wrapped around the levers and my thumb is behind the hood. There's no reaching for the brakes because my fingers are resting across the levers. Operating is just a matter of squeezing. I think people here are misdescribing the hand position, it's not straight across, it's diagonal.
Also, I compared to braking from the drops. There's essentially no significant difference, my fingers are at approximately a right angle to the brake lever on the drpps, maybe 75-80 degrees from the hoods.