Shane Black was lucky. Not to say that he's not talented, he is. But there is back story that most people don't realize. His agent took the Lethal Weapon script to Joel Silver, who worked with him to polish it. At the same time, Black was acting in "Predator", a Joel Silver production. Being a recent UCLA graduate with an agent who submits your script to a producer who is also producing another movie in which you're acting is a very rare alignment.
While "The Last Action Hero" is kickass, the original script was written by Zak Penn and Adam Leff. Shane was invited to re-write their idea in conjunction with two other seasoned writers. Often times, writers are called in to rework a script and go uncredited. It was not his own original idea, though his approach in adapting the screenplay by Penn and Leff was original. Plus this film was being directed McTiernan who also directed Black in "Predator" for Joel Silver's production company. So he was a known quantity when invited to come in and re-write a script which in part parodied his own work.
While the Blackisms may make some laugh, he was lucky it bypassed readers to go directly to a producer's hands. As a standalone spec, most readers would have rejected it outright. Hollywood networking can be a bit exclusive. Unless you have a direct connection to producers or are friends with known name actors or agents, you're better off following a more conservative approach to the spec script. If you are so blessed, you probably will have no difficulty getting any script reviewed by a key player--you are blessed.
