actually, linux will use a fallback method forauthentication, use the ad authentication by default, if the ad server isn't available it falls back to local file, so that the workstation is still usable even if the network is down. that is why the local account is required.
then there is the issue of you have to use samba client in linux to connect to a windows server, such as ad. the smbclient tools require a local user session to know what username and password to use for the remote server.
linux network server authentication to a UNIX server is much simpler and more transparent. the issues are caused by trying to connect to microsoft's proprietary smb protocol stack based servers from a unix like client.