Perhaps I didn't phrase my point well. If a merchant is comfortable with a higher risk threshold and decides not to go with ZIP verification then why does THAT merchant, not the others, bother asking for the ZIP if he isn't going to use it. That was my point and that only.

What have I learned from this thread. (Quite a lot actually so thank you to all who have posted.)
1. That I can prepay for more gas than I actually use and in the end won't be charged for it. I'll take your word for that but it would normally make me nervous.
2. This would have avoided my issue with leaving a card with the attendant. Something I would never recommend or do again.
3. I could try and play around with a variety of fake/ make believe ZIP codes but MMMV.
4. I could stick with my solution of prepaying gas at my rental company, my current preferred method because it is also more convenient.
5. US travellers have problems abroad because US banks have been slow to adopt CHIP & PIN.
5. Not everyone understands my sense of humour.


Please understand that from my perspective at least this was never about any perceived inconvenience in prepaying, having to walk into the store more than once, feeling discriminated against etc. In my case it was purely about avoiding getting my card cloned again and a genuine query ( since answered) about why the US was so far behind pretty much every other developed country with regards to adopting other apparently more effective securiy measures ( and I am no expert on CC security so I expect to receive more enlightenment if this assumption is wrong).