That's a good point. I think the interesting thing is that Android drivers do exist for all these device features, so any ODM that has an Android device could respin it as a Firefox OS device.
Right. As more of an enthusiast than any sort of developer (I've flashed my share of third party Android builds but never tried to create my own) I've always understood this to be why anyone can't just port the latest version of Android to a given device. Drivers need to be baked in and without access to proprietary driver code, you're still beholden to OEMs unless your hardware is supported by AOSP.
Firefox OS uses Android's kernel and userspace so it has just as many drivers as Android.