Umaid_Chakrani :
bios update will fix to support larger hard drives and newer processors and larger memory chips. You may need a bios update to support larger memories, new CPU's, or larger hard drives.
I knew all that - I specifically asked why for a GPU upgrade. As far as I knew, it was a mechanical interface with little work that the mobo does other than facilitate the connection (of varying size according to the mobo's specs) - a BIOS update wouldn't actually change any of that to my knowledge?