I can't see any reason why I'd want to allow both the grid and the form to edit the data. My most likely use case would be for the grid to provide an overview - that likely would not have a column for every field in the underlying data - and to use only the form for editing.
Whether the form would appear within the grid, as row detail, or below the grid, as in you synch demo, is, in my mind, purely a stylistic concern. Except, of course, that I'd not expect navigation controls on the form, if it was appearing as row detail. And from that it would follow that the insert and delete behaviors would have to be tied to the grid, and not to the form.
Still, I have been trying to get your synchronization example to work, and I've been having an odd problem with adding new records, that I have not been able to replicate using your demo code.