Because Skystar card works as a network device. Physical layer is DVB-S signal on 1.2 GHz band comming from parabolic antenna converting from Ku or C band via LNB. Data stream is only downlink (no uplink or packet acknowlegment) and there are used error-correction codes based on Reed-Solomon which help to recover data on reception side (sometimes it is not possible because 10 GHz Ku-band does not "like" heavy rain :)
I was using this card for reception of Meteosat images via EUMETCAST. Eumetsat distributes satellite data to users via a regular TV satellite (it was Hotbird6, not it is Eurobird9). So on the one frequency, there are many multicast data streams identified via Packet ID (they IP addresses started with 224.223.xxx.xxx). I was using Linux, so there were many virtual ethernet devices for each PID linked binded with Skystar driver and routed to final dummy0 device by smcroute. Special software Tellicast is used for storing files on disk (they are usually encrypted and you need to be registered and have a hardware key) and another software for data decompression and display.
More info about Meteosat reception is on my homepage: http://bruxy.regnet.cz/web/meteosat/