Australia Defence Association executive director Neil James said that some Australian soldiers were undertaking too many deployments.
James said the elite SAS regiment had suffered a disproportionate number of casualties compared with the rest of the defence force, because there were no alternatives.
"One of the reasons people are having to do, in our opinion, too many tours is there aren't enough of them and the reason there aren't enough of them is the defence budget is too small," James said.
The price of years of government underinvestment was being paid by "a very small part of the national family who are doing most of the country's war fighting", he added.
The Chief of the Defence Force, General David Hurley, said: "This man was a soldier's soldier."
He said it was "probably unusual" the trooper was on his seventh tour of duty, but he was confident Australian soldiers were not being asked to do too much.
Prime Minister Julia Gillard said it was a "dreadful blow" for his relatives, the nation and the Australian defence forces.
While the news might cause many Australians to ask why their nation's troops remained in Afghanistan, Gillard said the mission was critical to ensuring the country did not remain a safe haven for terrorists.
"We will continue our mission in Afghanistan even as we grieve his loss," she said.
A career soldier, the trooper enlisted in 1990 before joining the elite Perth-based SAS in 1995.
Defence Minister Stephen Smith said the death, the first since last October, would be felt deeply in the SAS community in Perth.
"Though one constantly says that one has to steel oneself for more fatalities, you can lull yourself into a false sense of security," Smith said.
Australia is due to start withdrawing its 1500 troops from Afghanistan in 2013.
- AAP