Short coated cats tend to shed much more then long hair. This is due to the life cycle of each coat type. Shorter coats stop growing much sooner then a longer coat. Thus, the short coated cats will shed far sooner then the long. In addition to this, the long coated cats tend to mat up when their dead coat does fall out. This makes professional grooming a very important part of a cats life.
The fact is, Cats do not clean themselves. They lick themselves, leaving their protein ridden saliva in their fur to collect grease, dirt, and dander. And they sleep with their humans? Yuck!
Having kitties professionally groomed not only keeps up on the shedding, but it also keeps the longer coated cats mat free. For those Persians and Persian mixes with the cottony hair, a Shave might be preferable to cut down on the amount of matting.