Part of the advantage to incumbents, I suspect, comes from the fact that a lot of the people, a lot of the time, are just not thinking much about politics;

This deserves a longer post, but for now I'd just like to say two things.

1. I strongly agree with Mark here. Most of the time, most Australians don't think about politics or our political leaders. The only times politics would touch on an Australian's daily life is at a hospital, waiting for public transport or experiencing brownouts during a heatwave. In other words, when things go wrong.

2. Most political journalists talk about a party's political "base" - the core group of voters who can be relied upon to vote for that party each election. The phrase "base" comes from the USA, where voting is voluntary, and a significant effort is expended each election "getting out the vote". With the primary system on top of voluntary voting, American politicians must appeal to their closes supporters in order for them to actually bother to vote on election day.

In Australia, with compulsory voting, there is no "base". Parties don't need to spend large amounts of time or energy getting people to leave their homes on election day to vote for them. They need to convince a large (and increasing) mass of voters that they should choose one party or another.

Thus, the politics of the "base" do not apply to Australian politics. Political parties in Australia instead appeal to the middle, rather than to one or more politically activated fringe (as in America).

With safe seats, and around 60% of the electorate solidly and reliably voting for one party or another, political parties in Australia have to appeal to the "swinging" middle voters. Thus, no "base" politics.