"The 'oo" weren't the most settled band, and Daltrey and Townshend had different ideas about direction and style which led to real fisticuffs (which Townshend invariably lost).
In one of the earlier (1980s) biography there's an interview with Daltry who was fired after one such spat in the late 60s, and he says that as he walked out he realised the only other job he could do was be a sheet metal worker - which wasn't that appealing.
So he swallowed humble pie, walked back in, and flushed all their drugs down the toilet as he wanted to be serious about it ...
... is sort of how it went.
He certainly kept his voice a lot longer than some of his contemporaries, so I'd say any stories of clean living could be true 
Sadly a lot of rock and pop singers never get a chance to look after their voices, with devastating consequences.
We saw Ian Anderson a few years back, and he hardly sang at all - there was a younger chap taking the strain.
That said, despite it being nowhere near it's peak, Robert Plants voice hasn't fared as badly as it might have ... well as of last November when we saw him (hometown gig 
)