@boomerang,
I've found may sites that say that many items, the most commonly used was most grains, create a pH embalance that causes the crystals to form in the bladder. The vet did give us a prescription dry cat food that would balance the pH. From what I've been told and what i've seen its much like poor eating habits in humans, most folks get away with it but a good percentage have problems because of it. Poor little guy spent 4 days in the hospital, iv's, catheters, anti spasmotics, antibiotics. He's home now but he's still not well. This threw him for a loop.