That's actually a bit of a myth. Some cats will but it's not that usual, most others will just crap where they see fit. We have 7 cats around us and for most of last year the little buggers messed my lawn up something terrible. Now that our cat is old enough to get out and is completely antisocial to all other living things, she patrols the garden and keeps the others out. And then takes a dump on the grass!
We have a fair few cats in the neighbourhood, I mowed our lawn for the first time this year at the weekend and didn't come across any.