Shaun,
Comparing my SS grate to my nickel palted grate on my performer, the rods are not as thick on the SS. It was also dull, not shiny when new.
Magnet test doesn't apply to the lower grades of SS. Put a magnet on a SS Performer table and you will see, although as Ray mentioned, it has less pull then steel.
Also, SS grates seem much easier to clean so far.