I think variation is in part due to doctors who set up clinics that specialise in infant circs and advertise their services. This would be true of Russell in Brisbane. The circ rate I'm sure is higher because of his promotion.
However, Russell has lied about the rate of circ in Brisbane, claiming it be 50%. I suspect lots of his clients come from outside the metro. area. Stats. for 2010 put the rate at about 16% for Qld. I lived in Brisbane for several years and very few people I know circed their children. The people I mixed with tended to be middle and high income families. A midwife who worked in a private hospital in Brisbane's wealthy western suburbs, where circ was available, told me it was rare for parents to circ.
I think it is entirely plausible that people who live in conservative rural communities, and the less well educated, are more likely to go with what they perceive to be the cultural norm,ie to circ. Granted, some people research and conclude there are advantages with circing, but most do it because that's what happens in their families and amongst their friends.
What is certain is that NSW has the highest circ rates in Australia. The large muslim population in the western suburbs contribute to this, but I have read in forums that most boys in the Newcastle area are circed. Wouldn't mind betting there are specialised clinics in the area promoting infant circ.