A surprising number of devices offer data acquisition over TCP/IP either in telnet, or HTTP get requests.
True, but all the Raspberry Pi's have atleast 1 USB port to which a WLAN adapter can be attached. Less cumbersome than ethernet cables, unless ethernet is mandated by competition rules or something. Of course, these may not be mobile robots at all, in which case ethernet makes sense.
Wireless isn't particularly reliable in all situations.