We had to restrict PM and editing permissions for new users as this was being abused by spammers.
When a person has been a member for a short while and made a few genuine posts then these privileges (and they are privileges, not rights) are assigned automatically. Spammers don't have the patience to wait for this.
Live links are another issue. Basically, they sap our bandwidth and unless someone pays us for this they are leaching off us. Live links pointing within our own site are OK of course.