I thing it breaks down like this (I'm sure Beck or one of the guys from the Analog Only forum will correct this if my memory is malfunctioning):
Simul-track means it is capable of simultaneous multi-track recording, but is not capable of syncing playback and record if you want to record (for example) two tracks now and two tracks later.
Simul-sync allws not only multi-track recording, but also provides synchronization between playback and record so you can sync recordings done in multiple sessions.
G.