Although specs put out by Ducati will disagree, the S has Marchesini wheels (non S has Enkei) and outside air temperature gauge (non S does not). Actually, this may only be the case on US bikes. Some of us US owners discovered that our non S's have Enkei wheels and no air temp gauge. The other market non S might have those items.
Other than that, yeah it's the Ohlins suspension and various carbon fiber bits, including the front (and rear?) fenders.