Be fair kenjit, ATC started introducing curved slightly tapered side panels to their domestic cabinets a few years back. You can be sure they did it for good sonic reasons.
It looks like ALL their professional speakers are boxes. We all know boxes are bad.
http://atcloudspeakers.co.uk/professional/loudspeakers/
Having curves doesn't stop it being a box. Its still a box. You gain nothing from having slightly tapered side panels. Its just cosmetic. Hence they do it on their hifi speakers because appearance is important to audiophiles.