This is a fairly wordy answer to your question, but bear with me as it explains a few of the assumptions made at the time.
The intent of the original legislation was to reward people who conserved power or invested in alternative energy sources such as solar, with an overall cheaper plan.
Maintaining access to the power network for an average urban home far exceeds the low user plan cost of $109.50 + GST PA ($0.30/day x 365), and with network access fees levied by the lines companies to the energy retailers not reduced by this legislation, retailers were allowed to increase the kWh rate slightly to offset the reduced fees collected from consumers.
The framework that regulates unit pricing for power and other factors, resulted in energy retailers being unable to recuperate the losses from the low daily rate user plans via slightly higher unit prices, which has resulted in profitable high volume user plans ultimately subsidising the loss making/marginally profitable low volume user plans. This was partly the intent of the legislation, however I think it is fair to say that the result was not quite what was intended, despite potential issues being singled to government at the time.
It is important to bear in mind that there isn’t a direct correlation between volumes of power used and the relative wealth of a household. In some cases low volume users are more wealthy (smaller family that perhaps use gas, solar, or wind for example) than high volume users (large family in a poorly insulated building). The opposite of this also holds true.
Around 58% of all households are currently subscribed to a low-user plan, however the phase out is supposed to result in 60% of households paying less than they do now. I do not believe this will eventuate.