[ben1040]

Unlocking the bootloader just allows you to have access to boot an unsigned system image. He points out in the article that you'd still need an image to boot.

With an unlocked bootloader, you could boot something that then messed with the filesystem to drop "su" out in the bin (and this is what happens when you boot a recovery image to root an Android phone).

But in order to do that, you'd need kernel sources, so that you could have something that would properly boot on the device and mount the filesystem.