That does sound less pleasant. Now that I'm thinking about that, I've encountered a system like that once. I think that was one of the first supermarkets trialing self-checkout. The system disappeared soon after and got replaced by what I've described.

It is quite easy to cheat the current system, though the random sampling helps some. I think someone somewhere made a decision that it is worth it to improve customer satisfaction and deal with some losses, but I have no idea.