From the original article link:

The study's co-author, Dr Cain Polidano?, who has two children born by caesarean, is also keen to reassure parents about the evidence so far.

"One thing we do know is that these effects are not going to be as large as the difference that mum and dads can make by providing and stimulating and supportive environment," he said. "That's certainly going to be more important than whether they had a C-section."

From an SMH article about the same study:

Professor Joel Bornstein, a neurophysiologist who co-authored the research, suspects that differences in babies' gut bacteria could be behind the delay. Dr Polidano (another co-author) hopes it triggers discussion about the risks of caesarean births. But he said providing children with a healthy, supportive home life always trumped any differences that arose from caesarean delivery.

The researchers tested the robustness of their results by excluding mothers with elevated health risks which led to caesareans and could impact a child's development. But the results remained the same.

The research is not conclusive enough to trigger changes to birthing practices, according to Dr Charlotte Elder from the Royal Australian and New Zealand College of Obstetricians and Gynaecologists.

Rise in Caesarean births in Australia

A report from the Australian Institute of Health and Welfare on Australia’s Mothers and Babies (2013) stated that 33% of women giving birth in 2013 did so via a caesarean, compared with 25.4% in 2001. This contrasts with the World Health Organisation’s recommendations that the caesarean section rate should not be higher than 10% to 15% (2015). It has been suggested that the rising age of first-time mothers is contributing to this rate but a study by Dahlen et al. in 2012 suggests that the private sector is also playing a significant role in the increase.

Source and here.

Some women are just "too posh to push"

My daughter recently gave birth to her first child via caesarian section, had every intention of having him naturally but problems with him being breech then turned manually then turning breech again shortly before birth resulted in a prolonged labour with limited progression of labour . .thus the only safe way out for mother and baby was an emergency caesarian..... 

Natural childbirth is torturous as far as I'm concerned and most women in a lot of cases  go as long as they can without screeching 'EPIDURAL!!!'....I was so ignorant of childbirth with my first child 40 years ago, I didn't even quite know what an epidural was . but I had one and they eventually with the help of forceps birthed a healthy 9 pound baby boy....

Women in some third world countries (and that includes women in PNG just a stones throw away from Oz) still die in childbirth and still have torturous birthing experiences 4 or 5 day labours ....Google 'fistular hospitals' ..

Yep some caesarians have to happen through emergency and there are a number of varied scenarios as I understand it ie. Placenta praevia etc.etc. but childbirth is painful and I thank god women do have access to safe pain relief.  Unlike in times past..