Norman- you couldn't extend this to WWII because that would imply a wholly different background where Japanese foreign policy had been more of a case of "oh come on, give us it, you know it's in your own best interests" rather than "we want it and we're taking it."
Japanese atrocities- an incidental point. I get the impression that during the war, America made more of a noise about Japanese treatment of POWs than Britain, but that this was reversed in post war years. America suffered more in relative terms if less in absolute terms than Britain (in round terms, US 7,400 died in captivity, about a third of the total, GB 12,500 died, about a quarter.) But after the war the "prisoner of the Japanese" cycle became a British staple, not an American. This is simply because America had Midway and the rest to look back on, Britain only the sideshow in Burma and Wingate's futilities. To distract themselves from the knowledge that they'd been pulled to victory in Asia on America's coat-tails, the British concentrated on the barbarity of the other side.
Unconditional surrender. In Europe, this was a way of keeping the alliance together. A perfectly rational one (no, I'm not going to reply to anyone on this.) Its extension to the Pacific was an automatic one, rather a considered view of the situation. In fact the Japanese surrender wasn't unconditional, quiet assurances were made about the Emperor's position. In my magnum opus (which I must resume work on), in an AH where America hasn't entered the European War, there is a compromise peace after the Japanese announce that the warmongering clique has been removed and committed "suicide", and the Emperor has abdicated and retired to a monastery in favour of his son. The trouble is that we tend to have this myth of undying loyalty and fighting to the last man among the samurai. In practise, you'd just as often have usurpation or the last minute deal between supposed enemies.