Smoking, Singing, and The Beatles?

Now everybody says that singing harms your voice rather than helping it, then how come Paul McCartney and John Lennon had great voices when they smoked a heck of a lot. It's a little more evident in John's voice that he smoked, but Paul McCartney still had a sweet, soothing voice even after 10 years of smoking. So can smoking help your voice or are The Beatles just lucky? :P