Actually, if it wasn't for exploits and security holes with Android, the Motorola phones wouldn't be rootable, period. To get AOSP running on them, you have to root the system and then use 2ndinit to hijack the Motorola init and boot something else instead.
However, on the Stratosphere, all I had to do was compile a new kernel. I didn't have to sneak around poking Android in different places trying to get through. This also means that an AOSP kernel can be compiled straight up to work on this phone. The problem with AOSP code and the Charge is the 4G radio hasn't been reverse-engineered yet like it has on the Thunderbolt. They had to do the same thing in order to get CM7 on there. If you look at all of Samsung's 3G phones - Captivate, Fascinate, etc... they support CM7 out of the box without a problem.
I'm not sure what you mean by "wild" things they do. They just use zImage instead of bootimg for the kernel, which packs the root filesystem a little differently... but its a supported way to pack a Linux kernel... just not the 'standard' Android way.