According to Australian IT:
Section 47 of the Act prohibits exclusive dealing which broadly involves one trader imposing restrictions on another's freedom to choose with whom, in what or where it deals. In some cases, exclusive dealing is prohibited outright and, in other cases, only where it substantially lessens competition.
eBay doesn't feel that restricting it's customers to Paypal will substantially lessen competition. They stand by their claim that the move is done exclusively to protect customers.
The ACCC is now calling for submissions (including from you), as to whether the move should be considered anti-competitive.
From the comments to the original story, it's obvious that a lot of eBay buyers aren't fazed by this. And why would they be? Buyers will definitely benefit from the added protection Paypal offers, without any significant negative impact. However, it's the sellers that suffer - they're the ones who will have to pay twice over to eBay to sell their goods, whether they like it or not. Even if you only use Paypal already, as a buyer or seller, taking away the choice of payment options and leaving only an alternative that will make eBay more money has to be seen as inspired by greed.
So, if you find this whole situation morally corrupt, make sure you let the ACCC know. But you need to do it by May 2. Hopefully the ACCC will sort this whole situation out in a way that benefits consumers, not eBay shareholders.