It sounds to me like any other kind of specification writing, simply from a marketing perspective. I can see the benefits, but eh. I'm not really convinced.
The benefits are to bring a clarity and focus to the product development process not always enforced by a spec. Who are you building this for as opposed to what are the features.
Writing specifications, and knowing which items in the roadmap bring the most value to the greatest numbers, are hugely different beasts. I definitely took the PR-driven approach to mean identifying those 2 items, even if taken by themselves (without the rest of the roadmap) they are meaningless. This is a massive, valuable skill to have...and one I'm not sure how to acquire. Don't know if this convinces you, but the article really spoke to me.
