At the end of the day, the entire health care (in what ever way its organised) is a cash cow. So its no real surprise that also the treatment of addictions is part of that business.
The effectiveness of Methadone treatment has been debated for several reasons, also here in Germany. Mainly because handing it out daily to substitute Herion is not really solving the addiction problem of a person, unless there is a proper anti addiction therapy going along with it. Which is even more costly, and often in short supply.
On the other hand, there are some positive effects of a Methadone program. Mainly, that addict are taken "off the street", meaning they dont need to commit crimes or prostitute themself to make money for drugs. And that they dont use dirty syringes. That helps to reduce further medical cost again, by avoiding Hepatitis, HIV and such.
Well, I guess its also a matter of mentality in a country. I'd imagine that in the US its seen less acceptable than lets say in central Europe. I'm not sure how people look at addictions and addicts in Australia.