I completely understand the difference between the two products. I've used both, though own neither.
They are two very different products but I maintain that they represent two different approaches to the same problem, pushing us past our current understanding of what I/O devices are. Google Glass is a push into the unknown, Facebook may not agree that it is in the right approach, but you are kidding yourself if they aren't looking at Google and wondering why they are not pushing I/O bounds as well. They're both looking for "the next smartphone", trying to determine what that will be.
The industry has been turned off of VR in the past by botched executions, and I am afraid it can happen again.