This Motherboard article is a fascinating look at Uber.
“I know this seems a misleading to you but it is meant as more of a visual effect more than an accurate location of drivers in the area. It would be better of you to think of this as a screen saver on a computer. Once a rider request a trip there will be actual information about the partners [sic] location showing up in the app.
Uber makes no distinction, visually, between the little black sedans that are available to passengers, and those that may be part of a visual effect.”