I know that.
PlexTools *always* need an update for each new drive since it uses blacklisting (like PX-708A2 and PX-714) and white listing (PX-712, 716, now 755) for Q-Check functions. PlexTools would have required an update even if the scan commands were the same.
What I wanted to say is that there is no reasonable reason why the commands should have changed, they simply seem to have. The only explanation that seems logical to be is that Plextor does not tolerate that people use pxlinux, qpxtool or pxscan with the px-755.