How did South Australia come to have smaller measures of beer? The "Beer in Australia" article on Wikipedia, includes a table listing the names for various size glasses in the different states.  One peculiarity is that some South Australian glasses are one size down compared to the equivalents in other states.

For example, it lists their pint glass as three quarters of an imperial pint (which would be called a schooner in other states that use that size), and their schooner glass as half a pint (which would be called a middy in a number of other states).

So my question is how did this discrepancy occur?  The Wikipedia page includes a number of references that indicate that these names have been used in SA, but doesn't indicate why.
In short, it's because of taxation. 

In the Commonwealth of Australia's Parliamentary Debates of 1904 (p.8534),  The Honourable Chris Watson (who went on to become the 3rd Prime Minister) made a statement about the brewers of Sydney strongly objecting to a proposal for an excise duty on beer. The sentiment amongst Sydney's brewers was that the additional cost would be difficult to pass on to the consumer, and in fact they had thus far failed to do so. In response The Honourable Alexander Poynton, said that the tax had successfully been passed from brewers to consumers in South Australia by making the glasses smaller.

For the record, The Honourable Chris Watson expressed sadness at the notion of smaller glasses.