That's how I think of a portal, but your definition of a publisher is different than mine. Essentially, I don't think any of the stuff you mention is necessary for a publisher, that's just how the big retail publishers happen to do things. To me, "publisher" implies just one thing, that they publish your game (ie. bring it to market; they get it distributed and making sure people know about it.)
In my mind, "portal" is specific to online while "publisher" doesn't imply either on- or off-line. "Portal" also doesn't do any marketing, while "publisher" does.
In my mind, "portal" is specific to online while "publisher" doesn't imply either on- or off-line. "Portal" also doesn't do any marketing, while "publisher" does.