They won't. I can barely tell the difference between my TF700T's 224PPI and my iPad 3 and definitely can't at 1/2-3/4 arm's distance. There is no way you are going to notice 10PPI when you get that dense.
The difference, if any, will be in the quality of the panel, brightness, any backlight bleed etc.
Amazon has stepped up big time but it isn't Apple who should be nervous, it's all the other sub-$300 tablet guys like Samsung and Asus who offer virtually identical platforms.
The Android market is saturated with products just like the phone space. It is really hard to carve yourself out marketshare and Amazon has the weight of its retail business behind it.