My first reaction to this statement was, "no that's wrong." But then on reflection, I think that it might be accurate. HOWEVER,
> Besides, the only difference between the two is whether it has customers
This is wrong.
The difference between a proof of concept and a product, is that a product is assumed to be reasonably safe. A proof of concept can be barely held together by string and tape. Because it's just trying to gage the reactions of the stakeholders. Or even exploring the feasibility of the idea itself.
A product had better get the edge cases cleaned up. If you write an email client that sends the user's password to some random URL, then that's okay because it's just a proof of concept. Nobody should be using it yet. On the other hand, if Microsoft's Outlook sends your password off to some random URL, then that's a serious problem. Because Outlook is a product.
Proof of concept has a "use at your own risk" or "for demos only" attached to it.
Product has a moral and ethical obligation of the manufacturer attached to it. It had better be reasonably safe to use for the intended (or reasonably accidental) usages.