I disagree. It's how the glass is attached to the phone. This is just a theory, but I've discussed it with People Who Know Things (TM) and they all have agreed

I disagree. It's how the glass is attached to the phone. This is just a theory, but I've discussed it with People Who Know Things (TM) and they all have agreed that it's more than likely a small sliver of plastic or glass (or maybe just a tiny dirt particle) has become lodged in the space between the glass and the phone during fabrication. 9/10 phones don't have these defects, but when you're manufacturing millions of phones 90% still leaves a lot of bad phones.