Node add & edit notifications should be able to be disabled by default

In the notifications fieldset on node/add and node/edit forms, the default setting is that notifications are enabled ("Do not send notifications for this update." is unchecked). As far as I can see, there is not a way to change that default.

In my case, I'm trying to set up a workflow whereby notifications for a node can only be approved by an appropriate role, so the default must be that notifications are not sent.