People who had amputated limbs had access to crutches and prosthetics, though. Meanwhile, dwarves have access to soap and an understanding that it prevents disease to keep wounds clean, which is part of why the Civil War had such horrific wounds.
Also, those "wounds" that actually get tracked because they went to the doctor are generally things like having a bullet in your bone causing a compound fracture, there. That sort of thing is lethal in DF right now. You probably won't even survive to get to the diagnosis stage, depending on how coy the doctor wants to be.
The sorts of wounds that had amputations were the wounds that had bleeding that was problematic to stop, and amputation was the treatment because you would just throw a tournequet around the whole leg or arm, and then write the whole limb off as dead, since that was an effective way to stop the blood loss. In DF, you almost certainly die of the blood loss before that point.
The treatments that are occuring in DF are treatments for seriously minor injuries that dwarves probably should be trying to "just walk off" rather than seeing those madmen with the bonesaws.
Crippling nerve damage, unless caused by something like a blunt shock in the right area of the body, should probably not be happening as frequently as it does unless you're already hitting the "wouldn't live to get to the hospital, anyway" stages of bleeding wound.