I have worked at companies that used VPNs. After you authenticated and logged with the VPN you had access to several resources with no further authentication. Granted I would always use the company issued computer so I don't know if there was another non-transparent authentication in the background but overall seemed that just being within the network was enough to access things.
Yes, with the (wrong) assumption that after you have connected to a VPN, all other services are free for the taking, without any further authentication.