While that is true (that Satoshi Tajiri is where he gets his name from), it has been "tradition" of sorts to always give the Event-Distributed Pokémon an OT which holds some significance to the plot of the movie, such as the "ALAMOS" Darkrai distributed a few years ago. Additionally, not all people (especially young children) know who Satoshi Tajiri is, but rather, just know and are a fan of Pokémon itself, and so to give Zekrom and Reshiram an OT derived directly from him wouldn't hold much significance. Given the sheer popularity of the animé, it would be expected, on the part of The Pokémon Company, and Game Freak, for the name "Satoshi" to be assumed to come from the animé protagonist, unless explicity stated otherwise.