TWA800 was caused by ignition of fuel vapour heated in an tank above the aircon units, so would naturally be hotter there - the centre tank on a 777 is apparently empty at the end of the flight, so both engines would be fed from the wings. These would be the cold bit, not being near any of the sources of heat in the fuselage.
Engine de-ice is apparently automatic, but remember icing is a function of meteorology, not temperature. There are certain bands of the atmosphere where it's more likely, which tend to be where turboprops hang out*, hence the highish accident rate of those machines to ice (I've witnessed this in summer on a hop over the Gulf of Thailand which was a worry). Up at 777 level the air's actually dry, so can't form ice. It is jolly cold though.
*
http://aviation-safety.net/database/...?id=19940225-1