I wondered the very same thing when they were introduced.
I have a friend who has very poor vision in his right eye, but normal in his left. Are they going to come out with glasses made for the left eye? All I have seen are glasses for the right. As long as these have been in development I can't believe no one at Google has considered this.
I asked my brother-in-law optometrist if he was going to start selling Google glasses with presc<x>ription lenses in them. He got a kick out of it and said he'd bring it up at their next convention.