Long before voters have to decide on how to allocate their preferences, the candidates have do theirs (known as voting tickets), which you'll usually have to search for if you want to know how they're distributed (they're not always made prominently public). These are how your vote gets distributed if you vote above the line. You can find the voting tickets published on the South Australian Electoral Office's website (within the 2006 election section).
The results of voting above the line can be surprising (remember how the Howard government got into power, with less than 50% of the primary vote—then then went about claiming they had a mandate to do everything that they wished to, despite the fact that the majority of Australia voted against them). You might vote for someone, because they're all you're interested in supporting, but if they don't get elected, your vote will get redistributed according to the candidate's wishes—which may be contrary to your preferences. These are major reasons why you should vote below the line, making sure that those you'd most want elected are placed well above those that you least want elected.
So how do the candidates come up with their preferences? They contact each other, promising to support the other if only they'll put them high on their preferences. Andrew's experience with this, over prior elections, has had several candidates promising him such placement, then finding out that they've put him last. It's obvious that they blatantly lie, just to serve their own purposes (i.e. they want others to preference them highly, and that's all that they're concerned with). Andrew, now, prefers to vote like everyone else—basing his preferences on his opinion of each candidate, not their desires for riding on someone else's preferences, and not making promises to support others in return for probably non-existent support for himself.