I (and I'm sure many others) did this for my Ph.D. project (group robotics) because it was the only way to get anything close to an acceptable frame rate on real time video using the ARM boards available. Colour processing is a big overhead, and the higher the definition of the camera, the worse it gets - so there's a definite trade off between the extra information from colour, and getting more frames/s to process. When you're extracting information from movement - i.e. the differences between frames, colour isn't what you're looking at in any case.

But knowing all that, and now knowing Tesla made that short cut, there is no way on the face of this earth I am ever driving a Tesla, or for that matter, driving a car anywhere in the USA that has them on the road.

You guys have a really good train network, right?

There are Teslas in many countries around the world, and autopilot is marketed as a feature in those as well.

About the US train network, it's good for freight but passenger trains are slow.