For the vast majority of people, higher rep ranges are more effective at building mass and lower rep ranges (with very heavy weights) are more effective at building strength. That's not to say that concentrating on strength doesn't build mass or focusing on mass doesn't increase strength, it's more a question of what is the best way of accomplishing your goals.
There are exceptions. People with unusually higher concentrations of fast-twitch muscle fibers will grow better with smaller rep ranges. And as you get more years of training under your belt you will be able to get results with fewer reps than you could when you had a younger training age.
We also have to consider the importance of changing routines (so called "muscle-confusion" strategies). If you are always trying to build mass, it will be easier for your body to adapt and stop growing. Even if heavy weights and low reps are not ideal for muscle growth, it can be effective at shocking the muscle back into growth.