I think that the other thing that comes into play here is the cost associated with the storage. Servers vs. Archival space. Sure, film will last 400 years. If its kept in a hermetically sealed vault with 24-7 temp and humidity control, say in a salt mine or something. With the quality of storage come costs. You certainly could store film cheaply, but you can store it expensively too.
I agree with the permanence of film, and its staying power, but I think the costs being given here are only a select example, and on that favors our side of the table at that.