I've seen pics of Franco and Arnold with 3 plates.
...Flex magazine adds the plates by photoshop.
Arnold did his rows with 2 plates and rounded his back. He didn't go above parallel so they still worked, but they work better with a continuously arched back and rowing to lower on the stomach... there's no need to stretch the lat at all in this movement; an arched back creates a strain on the lats even in the relaxed position.
There seems to be this assumption in bodybuilding that what the pros do must be proper training when in fact the opposite is often true... for example: Lee Haney may credit wide grip chins and pulldowns with his flaring lats, but we all know that clavicle-width/lat-attachments are genetic and wide grip rowing/pulling movements are less productive than the narrower grip alternatives yet greatly increase the risk of injury.
If I ever end up in a FLEX magazine training article I similarly could credit working on building sites wearing hob-nail boots with my freaky calf development... when in fact my whole family have exceptionally long calves and I don't even train mine.
For the record: Dorian and Ronnie only row in a semi-upright manner because of their enlarged midsections.
The Luke