From my time working in a MP's office the issue of the satellite service came up increasingly last year. Apparently the Labor government only purchased about enough "space" for 20000 or so subscribers at NBN speeds on various satellites that reach Australia.
They (or at least the NBN) then preceded to offer/advertise the service and naturally many people took it up (about 44000 to date). However, no additional bandwidth was purchased after the 9000ith subscriber. This resulted in a gradual slowdown in speeds as bandwidth was rationed to all subscribers.
I believe the coalition government is buying more bandwidth to help alleviate the problem but there simply isn't enough available infrastructure that is trained on Australia to lift level up to the advertised nbn bandwidth rates (at least til the satellites launch in 2015).
In the interest of fairness I will say I worked for a coalition member of parliament.
and here is the news article about the purchase of new bandwidth i tried to find earlier information about the over subscription but can't find the news story.
https://www.businessspectator.com.au...rural-services
http://www.smh.com.au/it-pro/governm...403-zqq1b.html