Due to issues we've had in the past and many, many arguments, as well as a lack of clear distinction between what may or may not qualify, webcomic characters are not allowed unless they have been published as a medium that can be purchased, eg. a graphic novel. When you start allowing webcomics, there's a chance of it potentially expanding into other online mediums, such as flash videos, youtube animations, NaNoWriMo/original fiction entries... stuff like that.

So basically, unless it's published like the rules already state, webcomic characters won't be allowed.