I believe I understand your question. You are confusing VPN Portal with a VPN Tunnel.
A VPN portal is just that, a portal, that allows you to access only specific web-based apps. You are limited specifically to what the VPN administrator is allowing you to access and use and is only for web-based applications. Not such a big deal in today's world where there are a lot of web-based apps (Sharepoint, ERP systems) and the user only needs to access these instead of their documents.
A VPN tunnel acts more like IPSec in that it grants you access to the network to allow for non-web apps to be ran to include printers and files. This is similar to IPSec VPN connections except that a client is not required to be installed on the machine, although, the SSL VPN may install a Java or ActiveX client at run time.
OpenVPN appears to be more of a content filtering bypass in countries like China that prevent internet users from accessing whatever they want. This would be more of a VPN portal in that is is more of a proxy than a traditional use VPN.