If I recall the registry does not charge the registrar until the names if confirmed and moved over. Seems most registrars have adapted the step of charging when the transfer request is submitted
It's easier to place the money in a hold status. And you are correct, the registry doesn't charge until the transfer completes. And by complete, I mean the registry is updated, doesn't necessarily mean it's in your new registrar's account (had some bad exeriences with "orphaned" domains with some companies).