Not all spammers are created equal? Some of them aren't too brilliant. Other like to build up a post count before they start linking to get around some of the built-in protections on some forums. Some forums prevent a poster from linking anything until they build up a certain number of posts. Just like the way our PM send function doesn't work until a noob reaches a certain number of posts.
Fortunately, we recognize most of 'em for what they are early on due to grammar, syntax and post content which often just smells funny enough to cause us to check the IP addy.
Made me laugh after our current conversation.