Stage Gate vs. Portfolio Management

One of the common debating topics when thinking about Portfolio Management is 'How does this interact with a Stage Gate process?' A Stage Gate process reviews a single project formally at a Gate Meeting and results in a Go/Kill/Hold/Recycle decision. The implication is that a project focused process determines whether a project should continue and can commit resources to doing so. In that case, what would be the role of Portfolio Management which is intended to make broad resource prioritisation decisions about a whole portfolio of potential projects.
This excellent paper from the Product Development Institute discusses the differing approaches and how they can be applied together. Thinking may have moved on a bit since the paper was published in 2001 but the fundamental descriptions and issues are well explained and still appicable.
Portfolio Management Working Paper