Having to show up means there is a compulsion in effect, whether or not you have to make a choice is between you and the piece of paper (otherwise you are violating another principle of a good voting system: that it is secret what you voted).
The situation (quoted from the WP page) is precisely this:
"Compulsory for federal and state elections for citizens 18 years of age and above. The requirement is for the person to enroll, attend a polling station and have their name marked off the electoral roll as attending, receive a ballot paper and take it to an individual voting booth, mark it, fold the ballot paper and place it in the ballot box."
So your participation in the election process is mandatory.
I'd wager the vast majority of the people so compelled to show up at the polling stations will actually vote. This should be easily testable. The proof would be that in Australia the total number of votes as a percentage of the population is high compared to other countries that do not have mandatory participation and that the number of blank or defaced ballots slightly higher than it would be in a country without compulsory voting (those would be the people actually using their vote as a protest vote).
edit:
http://www.idea.int/vt/countryview.cfm?CountryCode=AU (Australia)
http://www.idea.int/vt/countryview.cfm?id=216 (Thailand)
http://www.idea.int/vt/countryview.cfm?id=164 (Netherlands)
http://www.idea.int/vt/countryview.cfm?id=231 (USA)
Seem to solidly confirm my suspicion.
The situation (quoted from the WP page) is precisely this:
"Compulsory for federal and state elections for citizens 18 years of age and above. The requirement is for the person to enroll, attend a polling station and have their name marked off the electoral roll as attending, receive a ballot paper and take it to an individual voting booth, mark it, fold the ballot paper and place it in the ballot box."
So your participation in the election process is mandatory.
I'd wager the vast majority of the people so compelled to show up at the polling stations will actually vote. This should be easily testable. The proof would be that in Australia the total number of votes as a percentage of the population is high compared to other countries that do not have mandatory participation and that the number of blank or defaced ballots slightly higher than it would be in a country without compulsory voting (those would be the people actually using their vote as a protest vote).
edit:
http://www.idea.int/vt/countryview.cfm?CountryCode=AU (Australia)
http://www.idea.int/vt/countryview.cfm?id=216 (Thailand)
http://www.idea.int/vt/countryview.cfm?id=164 (Netherlands)
http://www.idea.int/vt/countryview.cfm?id=231 (USA)
Seem to solidly confirm my suspicion.