Actually Ferret has posted from 27 different IP's, and Metro has more than I can be bothered counting, the reason for this is dynamic IP's, each time you reconnect you are given a new IP.
ISP providers do this to save on IP's, no all customers will need a IP at the same time so sharing them around means they can make do with less, although given the nature of permanent broadband connections now this makes less and less sense, I have a dynamic IP account but they have made it static so it has not changed since I joined this ISP nearly 2 years ago, static IP's used to cost around $10 a month extra but now you can get them free from a lot of providers.
iiNet and Internode have dynamic sticky IP's so your IP can stay the same if you reconnect, you can force a IP change on those ISP's by changing your username in the modem from username@isp.com.au to username, or you could leave it disconnected for a few days (not sure if this works any more).