This actually seems to be really common with the pros. I also have a lot of equipment with weaker layouts. If a ball is already strong, you don't necessarily need to put a strong drilling on it to make it useful. When you've got a strong coverstock and a strong core, the ball is going to rev up and hook pretty much no matter what you do. You don't need to put an aggressive layout on the ball to kick out the corner pins on that kind of a ball.
The advantages of using weaker layouts on strong balls: energy retention, control, and predictability. Instead of reading the lane aggressively and moving hard off the spot like you'd see with a strong drill, a weaker drill lets the ball make a more gradual transition and roll off the spot when it gets into the friction. When the lanes start to dry up, carry down, or any combination thereof, the ball is going to be more predictable through the transition period and won't be as likely to get jumpy. To take advantage of the weaker drill, you will probably need to use a little more surface than you would with a stronger drill.
Of course, there's still plenty of use for stronger drills. Particularly on weaker balls, but even on strong balls. It's all about matching up what is comfortable with your game and using it in the right situations.
