Had the MDi to female USB come with my Scirocco and kept it for the GTD. With no Apple devices, I have no use for the blue collar MDI lead. Most of the time a memory stick filled with 320kbps MP3s is plugged in, but I can plug a USB to miniUSB lead into that.
No idea how much one would cost to buy from the dealership. I personally think it is a bit tight of VW to not give you both, or to at least give you the choice of one or the other.