That's true. The portal packages were experiments with what we could do using the built-in web browser to access custom services, because it's the only way in we have to the TV screen. At one time there was a way for Sky subscribers to access Sky catch-up services, because "we" found development links on the Humax servers and exploited them - they have since been turned off. There was also a means to access a web cam and put that on screen through the portal.
One significant advantage of a custom portal is to provide direct access to the standard TV Portal apps without having to go via the Humax screen (avoiding the load time, and potentially bypassing server failures).