Yeah, that comes up in the comments too (Sean Duncan notes that he co-launched the fansite Sherlocking before filming had even started), and for fandom purposes the Doctor Who pedigree of Sherlock's creators also played a big role (similar to how Dollhouse had a ready-made potential fanbase of Whedonites). Though in the franchise age, with all the sequels and spin-offs and adaptations and remakes of existing properties, that's not so uncommon these days. And I liked Stein's main point -- that not all forms of media fandom involve traditional fan fiction-centric style fan activity.