Pearlization is an additive like particles are.  It's finely ground mica mixed into the normal solid resin base.  Pearlizing a coverstock stiffens it so that it deforms less under the weight of the rest of the ball.  That gives it a smaller contact area on the lane, resulting in less friction.  

You can think of it like a tire that's over-inflated versus a tire that's got a normal or slightly less than normal inflation.  The over-inflated tire deforms less under the weight of the vehicle and gives you less contact with the road.  An under-inflated tire deforms more and gives you a larger patch of contact.

The amount of pearlization is, like the particle load, one of many design parameters that a ball designer has to work with.  More pearlization results in a stiffer, milder cover while less pearlization is more like a solid resin.  Some solids have a very small amount of pearlization, just enough to change the way the ball looks without it being considered a pearl (World Class Reactive, Big-R-Bang).

SH