Transorbs. To prevent excess static blowing the interface. I use them myself. I can dig out the exact one I use if required. I know they are made by Vishay.
Capacitors would slug the interface especially at full spped (USB2.0 @ 480Mb/s).
Transorbs appear pretty non existent electrically until there is too much static and then kick in to protect the equipment. Capacitors would have a progressive effect due to their frequency response.
From the PCB shown, they appear to be on D+, D- and Vusb to ground as best as I can tell which is the correct way to do it.
1=Vusb, 2=D-, 3=D+, 4=n/c, 5=0v