I've been filtered? Oh, that hurts!

Around the time Communications Minister Stephen Conroy began to tell Australia that the big ISPs were voluntarily filtering out net nasties I discovered I could no longer bring up a number of websites on the Internet at home, including the news aggregate site Kwoff.
Similarly The Political Sword was off the home viewing menu.
I did not connect these events and went hunting through my PC looking for what turned out to be a non-existent bug.
Because when I eventually changed my ISP to take advantage of better rates (leaving all my original operating and security systems intact) I suddenly found that all those sites which had been bringing up error and connection problem notices (and the odd verboten!) were once more accessible.
So what has been going on up in Dodo Land that innocuous web addresses are on some sort of voluntary black list?

Not A Paedo
Grafton