Can't they eliminate the manufacturing risk by outsourcing the hardware 100% to a company like ASUS that already has a working supply chain and significant experience with Tegra 3 and Android?
Yep. At the scale they are starting at, they can micromanage the control a bit, and team up with a company like ASUS to build the hardware.
Without having to embed a display on the device, I really don't find the price point of $100 outrageous -- aggressive, absolutely... but I am thinking they can probably make the lowest of the double digit margins on it.