Correct. It will never be possible to do firmware upgrades via the SD Card. The SD Card interface code and the FAT file system code is part of the firmware and is not available for execution while the firmware is being updated.
The USB comms is part of the boot block and operates independently of the firmware so USB comms is available while the firmware is being updated.
Regards
Paul
Figured as much that is why I threw it in there.
2005 1500 HD , Custom OS3 SD tune .
2006 Trailblazer Dinosaurs and Plants gave their lives so that we may drive , long live fossil fuel .