For adding content, regardless of whether the page exists or not, in both Obsidian and roam you’d have to do the same: Click on the link and type.
For the structure of the graph, it doesn’t matter if the pages don’t exist, they show up there, and they actually have an important distinction: Uncreated notes can be styled differently. If you have empty files, they will look exactly like any other node. Non-created files (or nodes) actually tell you visually that those pages don’t have content (because they don’t exist!).
You only need those 10 when you actually plan to add content there, and as I said above, to do so you’d do exactly the same in Obsidian and Roam: click on them.