You still didn't tell me why Australia banned and heavily censored games even after removing the guns? That's my entire point with this topic. Once a country gives in a little, they only keep getting things taken away until you end up with nothing.
Australia has actually started to relax it's video game censorship rules, even overhauling the rating system.
But the reason for the censorship is because the excessive violence, drugs, sex and so on wasn't deemed fit for children under a certain age, those same censorship rules exist in Europe, even in the United States. Aka. ESRB ratings... So Australia isn't unique in this aspect.
Note: The US does not have any video game censorship laws. In fact, the Supreme Court has ruled that video games are protected speech under the first ammendnent.
The ratings agency here is a private, voluntary one that serves an advisory role. Their ratings do not carry the force of law. Games do not have to be rated, and anybody is allowed to sell any game to a person of any age.