Small nitpick - many bank robberies are initiated and concluded just by passing a note to the teller without any overt threats, and without having any weapons on them. If they're savvy, they'll even ask for the money to be laid on the table to avoid the dye packs.
The popular portrayal of a bank robbery is dramatic but outdated.
I imagine that it's still a very threatening experience for teller. Much worse than logging on to a computer and discovering that there are money missing.