The reason black is used between the windows is for aesthetic purposes. It makes the vehicle look much sleeker with the glass blending in the entire length of the vehicle. This is true, especially if the glass has after market tint.
If mine get scratched or get the spider web look, I use white polishing compound, followed up with a good wax. Also I am very careful to only use the softest of cotton towels to clean off the wax. When dusting off the car with a "California" type duster mop, I am careful not to touch the black ABS plastic trim pieces.
Since the black ABS is also on the top of our center consoles and all 4 door switches, I have installed genuine stainless steel to cover those. There is no scratching those.
In the past, I have owned 2 VW, CCs, a 2009 and a 2013. Instead of using black plastic, they use metal panels that have been factory painted. There is no problem with scratching.