Well, my el-cheapo D-Terminal finally fritzed. The connections in the head must have had too much strain without the plastic covering that the original owner had.
First, I hacked the cable open.
If anyone does this, you only need the red, green, and blue cables and their outer shielding which seems to act as ground.
Here's the final product. Not pictured is the bright orange gaffer's tape that I used to seal things up. They work great!
So, final verdict once and for all: the D-Terminal is just a different termination on the component cables Nintendo sold in the USA.