Default Nexus wireless charger has a proprietary cable?

First, the Nexus wireless charger works fine with its own AC adapter, and also in my car with a USB car charger. Kill-a-watt shows a 6-watt draw, and the "Stay awake while charging" setting is ignored.

But the cable is short and very stiff, so I tried 4 different standard 6' cables and none of them will charge. So is the wireless stock USB cable proprietary?

I noticed many posts about modifying a standard USB cable for charging, but some are misleading as to the purpose. If you plug a modified/proprietary cable in your computer for data transfer are you at risk of shorting the motherboard?