You said "Terminal velocity of bullets fired above approximately 60 degrees is not high enough to be lethal." Mythbusters found that any angle more than a few degrees off of straight up (i.e., below 87 degrees) was enough to establish a ballistic trajectory and be lethal.
There is a huge difference in difficulty between 30 degrees, which is easy enough to eyeball, and 3 degrees which requires careful aiming with a specialized tool.
Let's take a common 9 mm round with muzzle velocity of 1,100 fps. When fired at 87 degrees, horizontal velocity component is 1,100 fps * cos 87 deg = 57 fps.
It will be much less than that on the way down due to air resistance throughout the flight, and negligible compared to terminal velocity (around 200 fps).
The reason perfectly vertical bullets are less dangerous is that they tumble and this tumbling reduces the terminal velocity below dangerous levels. Presumably tumbling could also happen at lower angles due to wind or other factors, it just is less likely.
It takes considerably more to kill someone than to break the skin. Maybe if you are laying on your back and the falling bullet hits the carotid artery, but this is a really contrived example.
There is a huge difference in difficulty between 30 degrees, which is easy enough to eyeball, and 3 degrees which requires careful aiming with a specialized tool.