Windows XP supported just one discovery method using network browser. This only identified windows PC and service running that service. Windows 7 and Vista support multiple discovery methods and detected other network services. These include network browser service, SSDP, and Web Services Discovery and UPNP. So more devices and servicecs are detected. For example if you windows media player to share media with other computers for multiple accounts. Then for each account you will see a listing under Media Devices.