They were understandable and obviously I'm looking from the always panoramic vantage point of hindsight, but in times of adversity selectors can either trust the status quo or attempt to inject new blood. The Aussie selectors obviously opted for the former (with the lip service of dumping the two-cap off-spinner for similar), which is perfectly understandable given how well the incumbents have served their team, but it was also predictable and safe. Even now, with a dead rubber on their hands, the only changes are those forced on them by injury.
It's better to fail trying something than just backing the house for me. Not to advocate knee-jerk changes either tho, which the dumping of Krejza looks a wee bit like anyway.
Hmm, looking at each of their selections separately-
Sticking with Hayden- fair enough, he had a fantastic record at the MCG and didn't look in especially bad touch- just kept hitting the ball in the air to a fielder (or running himself out). After his years of success at the top of the order it was reasonable to give him another game. Also if i'm not mistaken Jaques is still injured? So they'd have to debut someone mid-series against an attack of the quality of South Africa.
Sticking with Siddle- a selection i disagreed with at the time, because there are a fair few quality replacements about, but he bowled very well in the first innings here. If they decide he's one of the best quicks around, giving him the chance to adjust to tests is probably preferable to chopping and changing in the hope that someone has immediate success. It worked with Johnson. Plus it was at his home ground, which they might have quite rightly hoped would inspire him.
Sticking with Symonds when injured- A shocking decision on so many levels. Can't bowl, wasn't up to his usual standards in the field, isn't in great touch with the bat and in any case isn't one of the country's best six batsmen. Extremely poor from the selectors.
Switching to Hauritz- I think this one's been justified pretty well too, Krezja just went for too many runs to be an option on non-turning pitches. Hauritz had put in a good performance against New Zealand and kept it pretty tight, which was the role they were looking for their spinner to play. Picked up some key top-order wickets and as with Siddle, if Ponting or Hussey had taken their chances off Steyn, this could currently be looked like a great decision.
The Symonds decision was horrific, and if i made a decision that bad in any job i'd fully expect to be fired. But apart from that, they didn't do anything unreasonable- whether you agree with it or not, in each case at least it was a decent, justifiable decision.