While this topic started about tipping it also reflects what politics, policy, and legislation have done to damage the workers rights and this has led to the demand by workers for tips to help cover their needs.
No Centrelink do not always pick up the tab. There is a large under employed workforce that receive no Centrelink support for a number of reasons including parental income or assets, & income too high for receipt of benefits but still lower than the poverty rate. And the rate of income in Australia to put someone into the poverty region here (relative poverty) is different to what it is in the States.
Comparison with pay rates in the USA is perhaps not the best way to interpret what is fair or right. Many there are also below what would be considered fair rates of pay and it requires people to work extreme hours just to survive (and not very well at that). Do we want that system? Trickle Down economics among a number of other US policies is shown to be a failure.
As @TheBBG states the Governments over a long time have destroyed what we used to consider fair pay for fair work. Some of the signs of that failure to address the off kilter policies is increased casualisation of the workforce, unfair rates and rights of employment, homelessness, debt stress and many other socio economic concerns. If workers were given fair pay then they would pay more tax, spend more thus increasing profitability of businesses, invest more, improve the superannuation savings, likely not require or demand tipping, and it would also help reduce the burden on Government paid benefits for all sectors including Age Pension.