Perhaps there's many subcribers to your ISP that are running what is known as an unsecured proxy or open proxy. It's basically a networking software that hasn't been configured correctly by it's owner and it is a way in which IRC users can mask their real address with. If this happens too often then opers tend to get annoyed and make stronger bans to lessen the incidence of naughty chatters being able to connect with a falsified address.
Masking one's IP for the purpose of avoiding a ban or making it hard for staff to lodge formal complaints is universally considered lame. Unfortunately there are innocent people that get affected too.
