Is that really true? The gas stations around me (in the middle of a city) are generally pretty empty inside, but full of cars filling up. They also sell gas for a few cents higher. It seems like it's a mix of the two strategies.
IMHO the charger networks are a short-term solution and will ultimately go away. It's not that they are all making money by marking up electrons, it's that they're inconvenient.
I know people that have "all the apps" installed on their phone because they want to use whatever charger is nearby, not necessarily one on a particular network. As these things become more ubiquitous, people are going to want to pay via cash or credit in addition to using their phone. Your local restaurant doesn't need their chargers to be on a national network, they need them to be run by a local guy who also handles maintenance - like arcade game operators in the 80's or your local vending machine company today.