You will also see a round design in many of these chairs, if you take a look at the chair itself the wheel base and foot rests should be more circular than their square counterparts that have protruding leg rests. The round shape makes it much easier for the user to judge how big the chair actually is when maneuvering!
These seats are manufactured specifically for the outdoors. Dragging your indoor chairs outside will do you no good. Using these pieces is way better for they can endure long exposures to harsh weather conditions.