All true but (I'm partly playing devil's advocate here) ...
If there are several fields being updated, the control before update event will of course, only cancel the change in that one control, whereas the form before update event will reverse all change made to that record.
It could easily get very confusing if both types of event are used in the same form.
More for interest than anything else, I've attached a very basic example using before update events in both a control (Input1) and the form. Both have message boxes so its easy to see which event is which. In this case, there is no validation involved.
The control event is triggered first on leaving that field then the form event on leaving the record. Even if the control field change is confirmed and then the user changes another field before moving to another record, both changes can be reversed in the form event
BTW: The Almost Impossible DB name is not an indication that it is complicated. Its the username of someone I was assisting at the time!