As fabulous as I think John Simm would be for Littlefinger, it's sometimes not so easy. He could easily be committed to other projects or even not interested in the role. Even if he has auditioned, or thought about auditioning, it's possible that his tape doesn't speak to the casting director in exactly the right way. Hundreds of things can go wrong in casting, but hundreds of things can go right as well. I think we'll just have to trust HBO here, who usually have an excellent feel for putting the right man in the right part.