1) Google can (easily) make the argument that it needs to sample the image stream from every headset along with GPS/gyro to recognize "what you are looking at." These samples would be stored (of course).
2) Each sample can be OCR'd to recognize signage and contextual strings for searching that particular frame (e.g. thinking of every frame as a "web page").
3) Google can then "index the real world" with the image and contextual data.
Forget sending cars around taking photos. With enough users wearing headsets, Gooogle can build a searchable, virtual representation of the physical world.
And to get back on-topic: I'm surprised that the Word Lens guys didn't think of this (not the image mapping, but the signage/contextual mapping). Or maybe they have...