The Amazon chart this month will be skewed low for PS4 compared to NPD because NPD will count the Batman bundles for June, whereas on Amazon all those bundles appeared in the April monthly. There will probably be a bit of a spike in the Amazon chart when Batman releases, but not as much as would otherwise be expected with a large number of consoles already pre-sold.
OTOH Xb one could see a relatively larger Amazon spike when Batman comes out because no one is pre-buying Xb ones for Batman, all the Xbox fans of Batman will buy their Xb one the day / week Batman comes out. I don;t expect this to put Xb one ahead of PS4 in the monthly chart, but I do expect the Amazon chart to look a lot closer that what NPD turns out to be. I don't think we'll see a 2:1 month, but I think there will be plenty of daylight between PS4 and XB one for June. MS could do something to try to counter Batman on PS4, but I don't think it would be worth the effort and expense just to boost sales in a normally low selling month.
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