Yeah my grandma says the same thing, except she says it about Blue Plate. Dunno if Blue Plate mayo is sold anywhere but the South, but she is rather adamant about this. Only Blue Plate is the REAL mayo for her.
Duke's[SUP]©[/SUP] is the more prevalent brand down here tho; most 'regular' grocers don't have Blue Plate[SUP]©[/SUP].