He wants to sell his coins. Imagine the panic if those coins started to move without notice and without people getting used to the idea that satoshi might need to cash out. It would be pandemonium.
This is a possibility... Maybe the Australia government already found out he is Satoshi and asked him to pay for the US$450,000,000 income tax. The only way out is to sell the coins to cash out... unless oz government is "Bitcoin Accepted"...
I think in Australia you only pay tax on the capital gains if you sell your coins.
I think the scenario is more like the following: Imagine you create an amazing technological breakthrough, the breakthrough of the century. You are feeling very good and decide to walk away, leaving coins unsold, to do another project. At this point you are feeling invincible, so it's easy to leave the coins untouched, because *of course* you'll have other breakthroughs and make money. But none of your other projects work out. Meanwhile, there are the original coins from your original project, just sitting there. And you think, why am I being a saint over this? This is my invention, that is my fortune.
So you decide to come out and say who you are in preparation for selling your coins. Only the community is furious. Because they believe greed is good only when they are accumulating coins, and they want BTC to go to the moon - but for that to happen they need Satoshi to stay poor and selflessly refuse to sell any coins for the greater good of making every one else filthy rich! Hence the scream of fury we hear...!