There are unsurprisingly plenty of studies in this area. The article you quote is one. However note it says "Long-term marijuana use can lead to addiction" not "Long-term marijuana use leads to addiction". The results very from person to person.
Here is another article: from the University of Wisconsin-Madison:
The majority of marijuana users do not develop addiction: they do not experience loss of control; they use when they choose to, in the amounts they choose to, getting the results—in general—that they intend to get. [...] But just because addiction doesn’t occur in all users, or even most users, doesn’t mean that addiction doesn’t happen to any user. [...]After an initial period of stable substance use, the user will begin to lose control. Others will comment that there is a change in the user—and the user will at first deny or rebut such concerns. Use will continue despite the problems it has caused. Larger and larger amounts of the substance are used, consuming money that could go to other purposes, and the person may spend more and more of the day or the week either using, thinking about using, or arranging to get more supplies of the drug.
The Harvard Mental Health Letter says:
Observational studies suggest that one in nine people who smokes marijuana regularly becomes dependent on it. Research both in animals and in people provides evidence that marijuana is an addictive substance, especially when used for prolonged periods.
This article from Psychology Today has a quote:
The Science of Marijuana is written by Leslie L. Iverson, a professor of pharmacology at the University of Cambridge in England. In the book, he reviews decades of international research on marijuana, both laboratory research and survey research. Based on his review of the scientific literature, between 10 to 30% of regular users will develop dependency. Only about 9% will have a serious addiction.
Here is another from Brown University:
No one would argue that marijuana is as addictive as alcohol or cocaine. However, it's wrong to say that it is not at all addictive. More and more studies are finding that marijuana has addictive properties. Both animal and human studies show physical and psychological withdrawal symptoms from marijuana, including irritability, restlessness, insomnia, nausea and intense dreams. Tolerance to marijuana also builds up rapidly. Heavy users need 8 times higher doses to get the same effects as infrequent users. For a small percentage of people who use it, marijuana can be highly addictive. It is estimated that 10% to 14% of users will become heavily dependent. In 2006 marijuana was responsible for 16% of all admissions to treatment facilities in the U.S. Because the consequences of marijuana use can be subtle and insidious, it is more difficult to recognize signs of addiction. Cultural and societal beliefs that marijuana cannot be addictive make it less likely for people to seek help or to get support for quitting.
The consensus is that many people can regularly use Marijuana without becoming addicted. However there appear to be some people who can become psychologically and physically dependent on it.