It does look like the vendoring stuff is only there to satisfy backwards compatability, not for new usage. It's supported but now I've gone to look there are some caveats in the docs and on the wiki, hinting that you shouldn't use it. Files in vendor are ignored it seems unless you pass a special flag, so a lot of people are going to be very confused (including the author of this article). The communication around this tooling change have not been great, and that's why guides like this are springing up. Now that it is getting more complex, Go could definitely do with some more short and simple getting started guides from the Go team, for specific topics like versioning, where people also bring in their assumptions about how things work from other tools.
Since this is still in beta, and seems pretty half-baked, I'm not going to touch it for at least another version of go, but hopefully once they have the kinks worked out it'll be a reliable method to specify dependencies that everyone uses.