Have a look at the fact sheet for the changes, set to come into effect sometime after Sept 1st
http://auspost.com.au/media/documents/Reform-Fact-Sheet.pdf
Also, an interesting news article:
http://www.smh.com.au/federal-politics/political-news/abbott…
"Mr Fahour also defended his salary of $4.6 million a year - the highest paid public servant in Australia - saying 75 per cent of Australia Post's activity was commercial logistics and it was a "highly successful business". The latest annual report revealed 409 managers and executives at Australia Post were earning more than $195,000 a year"
I'm not sure how slower delivery would save any money, would require the same amount of processing time etc.
Unless it's not designed to save money, simply make money by getting people to pay extra for 'priority service', which is just the same speed as now.