That's true to some extent, Ixis, but my point is that drugs are not a cure for boredom or emotional problems, and in my experience it's the people who try to use it as such that end up hopeless addicts. Believe me when I say I've used plenty of drugs, I don't try to mask that, and I've tried things that most people consider dangerous and some idiots claim are instantly addictive. I've never used drugs to avoid issues in my life, though, and I believe that's part of the reason I don't have a problem with them. It's been a couple years since I used anything besides alcohol and I've probably had a drink less than a week's worth of nights in those past few years. That doesn't mean I won't do them in the future, either. But most of the people I did drugs with or drank with are still doing those drugs, because they have things they want to forget or avoid that come right back every time the drugs wear off, or simply because they're bored and drugs are the easy cure so they don't ever try to look beyond them. I don't want to sound like a dick, but I don't think most people have the maturity or discipline that's kept me from falling into that same pit.
As far as the difference between endorphin rushes and drug addictions, first you have to qualify it with the statement that some drugs simply aren't chemically addictive in a meaningful sense. Cannabis and most hallucinogens will not produce any chemical addictions, though they can become the objects of obsessive behavior the same way any other normal activity can. Other drugs though, like alcohol, opiates and most stimulants do effect chemical changes in the body and create a dependency wholly different from "addictions" to things like World of Warcraft or sky diving. There is a point where the chemical cycle can become so imbalanced that ordinary behaviors result in physical addiction but it's pretty rare, I think the only reason we see so many examples of it is because of the sheer volume of people in the world. If you look at the numbers of morbidly obese food addicts, real video game, porn, internet, or extreme sports addicts, etc. vs. the number of people suffering from real chemical addictions it's pretty clear they're an exception, not the rule.