Airbus produced an article in one of their magazines some time ago criticizing some of the ETOPS terminals used for diversion when Boeing were looking to extend past 180 mins. The North Pacific ones in particular. The handling of the passenger load in extreme winter conditions was a factor that they emphasised if the aircraft was unable to be used and kept warm enough at the remote small stations. Obviously four engines better than two from their piont of view.
I presume that on the Europe to Western North America Kef, Sondrestrom,Iqualiut,Churchill etc can feed and water a full A-330 load.