if we really wanna get techincal the "stepside" was the normal bed side back in the day it originated from how the running board on the fords went all the way back to the fender like so:
because the pickups used the same rear fenders and running boards as the coupe's to save on $
now in the later years people liked the step because you could get things out of the bed so they left it as in so:
How the styleside originally started was with the Casket bed or better known Flower bed.. they used the wide beds for hauling caskets or flowers in the funeral, Very rare beds only seen about 4-5 in my life so far being in the Model A club.. also this model used the tudor and sedan model rear fenders because there about 3-4" less wide...
that styling later led to the styleside because it was wider and could haul more good's like so:
but in 1959 you could still get a step side bed as in here:
for the F-series line after 1986 its hit or miss on getting a stepside they offer it here and there...
where as for rangers it didnt start till 1993 after the 3rd gen's where introduced with the splash they kept the same bed unchanged untill 2004 was the last year they produced it after that 2005+ there was no step side
your Mazda Dual sport bed came into play in i think 2004 on the STX its hated by alot of people some love it but not many...