Nah, you are talking about different things. You are talking about pay at the pump like a lot of Supermarkets let you do (or force you to in the case of ASDA), what Chindie is talking about are normal garages that won't let you put fuel in, until you walk in and pay for the fuel before they turn the pump on.
You are right though about the pay at pump one, Tesco reserves about £100 from your account and it can take hours for the balance to be returned, so I always just walk in and pay at the supermarkets (and hence why I don't use ASDA)