Braking on a vintage road bike
It is true that the old style brake levers were not as powerful from the hoods as modern ones. The reason is geometry. 

The picture below shows how old and new levers move when pulled. With old levers, braking from the hoods requires one to pull back and push down at the same time. As said in comments to other answers, this is doable but not very effective or intuitive. With new levers one simply pulls the lever towards one's hand. The small blue arrows show how brake cable moves.



If you want to improve braking on the bike and don't require complete authenticity, there are aftermarket levers with modern pivot placement.