Apparently something similar has happened at at least two other mosques elsewhere in Australia in the last few years. Luckily it hasn't led to much trouble, unlike the publication of certain cartoons or release of films. Perhaps the media is making more noise about it than anyone else. While the apparent intent behind throwing a pig on the grounds of a mosque might offend some Muslims (e.g. the message of "you're not welcome here"), the act in itself does not render that place unholy or impure, nor does it send any constructive message.
I'm sorry to say it, but I expect this stuff to continue. If the experience in Europe is any guide, the political demands of Muslims will intensify as their population grows, which will add fuel to the fire of "haters". This is not helped by the general image of Islam which media reports of the last decade have helped to create, rightly or wrongly. Differences in world view can easily become the basis of manipulation, as those who like to divide and conquer would know. When people express their opinions, I hope they are pulling their own strings and not having their passions stirred up for them. This applies to both sides.