First, it actually does have fastboot oem unlock, and no: there is no "specific command in adb" to unlock it; the command you are seeing people post reboots the device unto the bootloader, which can then be used with fastboot oem unlock.
However, that isn't helpful; in fact, I had to use an exploit (not one I came up with: a known one that affects all Android 4.0/4.1 devices) to accomplish this. (So, my device actually still has a locked bootloader ;P.)
In order to go from "unlocked bootloader" to "root" you need a new image to flash. The most common way to get this is to dump the kernel from the device (as you know that that works), but guess what: you can't, as that requires root.
The alternatives are either to have a stock image from the manufacturer that you can extract a working kernel from (something Google did not provide for the Glass, at least yet) or to build your own from the Linux source code.
Building your own kernel is, of course, possible, however it is quite irritating, and there is no guarantee the result will work as there might be binary blobs in loadable modules that you need, or other irritating hardware checks.
You also need a good feel for what hardware the device has for this to be an option, and Google disabled access to /proc/config, which makes the process of building a vaguely compatible kernel all the more like guess-and-check.
So no, it isn't at all clear to me that it is so obvious that you can go from nothing to "modified software" on the Google Glass. I'd like to see Tim Bray explain how he'd easily go about hacking on the thing ;P.
This is especially the case as the Glass Guide (the fancy term for the Google Glass sales person) who gave me the glass (I chose the option to go to Google HQ to pick it up in person) seriously told me that the debug mode feature (which gives you adb shell) is something that he thought they removed from the units they were distributing. (I guess I was the first person to find it during the at-Google demo and then ask what it would let me do ;P.)