I doubt there is any industry conspiracy here re: drugs. Rather it's just one of those industries where drugs are commonplace just as with media or the city. Though a broker/banker going off the rails won't likely make headlines (unless they jump off a tall building). Still a large part of it is simply down to the people you end up surrounded by and of course your own personal descisions.

Pop stars, advertising execs, brokers and kids growing up on council estates in Glasgow all probably have a higher chance of being around people who who indulge in drugs. How they deal with it is still down to personal choice - I don't think celebs are necessarily a special case on their own here rather they're one of a few groups with a higher risk than normal. It's still down to personal choice/descisions but having a partner with issues in addition to a social circle that are indulging in it probably puts you at the greatest risk of ending up with a problem yourself. She certianlly seemed to be in such a situation and that sort of situation could well have been enough to effect someone who might otherwise have not developed a drugs problem.

That's really the crux of the problem, the music industry is just as bad but it will never make headlines either. I've seen first hand at afterparties bands, artists and execs all gathering round for a snifter or a toke on one thing or another. If you are surrounded by these people in these sorts of environments all the time I guess even with the best support in the world you won't be getting away from it easily at all.