technically its cutting paying gst on the excise (ie, a tax on a tax), and the goverment is talking about doing so because
a) they want to appear to be doing "something" about petrol prices (and they currently have budget surplus, although i think spending it on upgrading our train system would be a much better thing to do).
b) during and since the last election both parties have been saying they would (although the current opposition were talking about cutting the excise itself by 5c, rather than removing the gst on excise, which ammounts to about 3.5c).

Andrew