Not entirely pointless.  The "auto-troll" was the type of person who infested these forums last year and the infestation was pretty bad.

Troll creates and account, blatantly spams and trollers, gets banned, creates another.  The zero cost means they would make dozens and dozens of accounts.  This makes trolling require at least some "work".  Trolls tends to not like the working part.  Even if they make one accont if it gets banned 10 minutes out of the noob zone they tend to not make as many accounts.

Your logic is like saying "Seatbelts don't save 100% of lives therefore seatbelts should be removed".  The stats show the noob rules reduce (not eliminate) the amount of trolling nonsense among new members.