Actually looks quite neat... I did consider that idea a few years ago, but because the seat belt guide isn't straight edged, and that clip is, it doesn't provide equal support along the length of the sides. You can see what I'm getting at if you look at the pic, you can see the straight edge of the clip sticking out from the curved edge of the seat belt guide at the corners. Also, the bending requires really accurate tooling, which makes manufacture expensive.
But each to his own I say...