As near as I can tell, the Australian IOC's position was that, since there was no official recorded blacklisting of Peter Norman, there's no proof it ever happened, and they shouldn't have to apologize for something that didn't happen.
There was no punishment dealt out to Peter Norman following the 1968
incident with black power salute. He was not punished. He was not
ostracized. He was not blacklisted. He wasn't even reprimanded by the
Australian Olympic Committee at the time. ...
We're a little bit baffled by
this debate. We never had an issue with Peter Norman. He never had an
issue with us.
There was never any suggestion that he was ostracized or not happy
with the AOC. We've got nothing to apologize for because we've never
wronged Peter Norman.
The assertion that there was "never any suggestion that Norman was not happy with the AOC" appears to be quite false, and much of the rest of the quote is implausible to the point of being humorous (supporting material below the fold line, as its bordering on off-topic, unless you are inclined to believe the humbug quoted above).
So while I don't think its possible to get perfectly into the heads of the AOC, it does appear to be clear that in 2012 they were not yet ready to admit their organization had participated in the ostracization of Peter Norman. Some of this treatment had been quite recent (only 12 years past), and thus at least a few of the perpetrators likely still had positions of power within the AOC.
One important thing to realize is that Australia at the time was living under a set of laws with respect to its own indigenous racial minorities that were rather similar to Jim Crow and Apartheid. (In 1968 it is said that the Australian census counted sheep, but not aborigines). So expressing any kind of support for racial equality in such a public way was not likely to be well-received by the power structure at home.
Not only did Mr. Norman complain of qualifying for the next Olympics 18 times without getting invited, but he said he had a lot of trouble even finding anyone who would hire him (exactly the treatment Carlos and Smith received upon their return to the US). He ended up a gym coach for a while, and finally a butcher. They report that during this time he was invited multiple times to condemn the gesture of his fellow athletes, and consistently refused.
In the 2000 Sydney Olympics, all of Australia's other past medalists were given a "lap of honor". Peter Norman, their greatest sprinter ever, wasn't even invited to attend. The US delegation was so incensed by this that they invited him to join their group.
As a counterpoint to the photo above, I can't resist posting this later picture of the three, from Norman's funeral.
Photo: Wayne Taylor