Was that for private vehicles that people bought themselves and paid for the fuel and electricity themselves? I remember a few years ago a study out of Europe of plugin hybrids that found the drivers didn’t plug them in. One the details came out we found that those were corporate vehicles assigned to them mainly for business use. They were reimbursed for gasoline purchases but were not reimbursed for electricity. The result was that they chose the option that results in less personal cost to them.

I find it hard to believe that people will elect to spend more money on a plugin hybrid and then not bother plugging it in as long as they have an easy access to a power outlet. Just the extra cost of gasoline in that scenario should overcome the minor effort of developing a habit of plugging in when you get home.

Maybe now with gas above 2€/liter, we'll see more people charging their PHEVs. However they are also a rich person's toy, since you need to charge them at home to have the battery-powered miles be cheaper than the petrol-powered ones ergo you need a home with a garage.

At public chargers you pay much more than at home per kWh. On top of that, they have been incentivized (0,25 Regelung) for companies as fleet cars (Dienstwagen) and companies give out free petrol so you have no incentive to charge it at home using your own electricity when you can just fill up otherwise with free petrol.

easy solution: expensive gas.