I'm not a shipping pro, so I'm sorry I can't give you an informed answer. I would assume that the configuration is what works best for Matson, logistically. The company does have a ro-ro barge (see pic of WAIALEALE). Maybe one of the other forum members can chime in?
weeboopiper thanks for your information, I found the Waialeale but thats really just a barge with an engine. The ships I was thinking about were small Around 120-150 containers but the containers came on board the ships on trucks and were picked up by the crane and the trucks drove off again. Accomodation block had a huge drive through tunnel reached by a ramp.