The way that I've explained it to people is that the Nazis could, especially if the Soviets fell, reach a point where they would have been very difficult to dislodge no matter the economic advantages that the allies had over them. The Japanese, OTOH, could never really reach that point. Even if Australia and India fall (either of which are much less likely than the USSR falling to the Nazis), the Japanese while they would have had more oil would have had *extreme* difficulty turning those conquests into additional ship and air capability. And without that, the US *can* sail to the Japanese coast and wreck the country. And while I have no idea what a significant stranged IJA in Mainland Asia would do, it wouldn't survive long.Jon Parshall is in the right of it in saying that Midway did not decide the war, but that it did change the course of the war. In the crude sense, Japan lost the war the moment the first bomb fell on Battleship Row.
A big loss at Midway would likely have made some butterflies in Allied grand strategy in 1942, but not enough to alter the outcome. I have long been tempted by the thought that a loss at Midway not only would not lengthen the Pacific War, but might even shorten it. Because you'd be butterflying away the Solomons Campaign, and it could be that the smashing up of the IJN that took place in the Solomons over 10-12 months would just happen more suddenly in the Central Pacific once Nimitz started his drive.
Parshall's classic essay over at CombinedFleet is essential reading here: http://www.combinedfleet.com/economic.htm