This is a very unusual list. NYC is definitely cheaper than Melbourne.
I can live in Brooklyn Heights cheaply and commute to Manhattan for work in 20 minutes. I can eat premium angus or kobe beef for US$50 whereas it'll cost me A$120 at Rockpool in Sydney/Melbourne/Perth.
Oh and I can buy a decent house for around US$1m, while in the equivalent in Sydney - say North Sydney - it'll cost me A$2m.
Also I am surprised not to see Oslo, Copenhagen etc make top 10. They are traditionally regarded as two of the most expensive cities followed by the likes of Moscow, Tokyo, Hong Kong. The next league is usually then Sydney, Shanghai, Beijing, Singapore etc and then Melbourne, Guangzhou, Shenzhen, Perth, Brisbane, Adelaide etc. And Port Moresby?!?!
The Mercer list I saw a while back makes much more sense.