Two riders putting in the same mileage in the same weather, one without brakes and one with at least one brake: the rider who only uses back pressure and skipping/skidding to stop is going to need to replace his or her chain more often.

Doing 100-150 miles a week brakeless in NYC, I am apparently supposed to replace my chain about every six months and I'm riding the KMC Kool Ultra-light chain. Better than messengers here, some of whom apparently replace their chains every month. Probably because they ride 40 to 100 miles a day.

Park sells a handy tool that makes it really easy to know if you are one-quarter/half/three-quarters through the life of your chain. Or just plain in need of replacing it.