I've heard the same sentiment expressed by all sorts of people in all sorts of callings. Writers, yes, and also doctors, lawyers, musicians, artists, schoolteachers, scientists (that's all I can think of off the top of my head but I might remember more if I gave it more thought).

But I've also known an equal number of shiny happy people in all those professions, with lovely relationships and no drinkie. Many of whom connected their success and happiness to their callings.

In short, it's a lovely quote, but I don't think there's data to support the generalization.

(Interestingly, I saw a documentary a few months ago on the high incidence of demolished families, drug/alcohol abuse, angst, insanity, even suicide -- among mathmeticians!)