I heard that a lot, but are we sure about this?
Petrol in Europe is taxed at about 50%, but is almost exclusively imported, thus this is the only income for gouvernements.
Electricity, on the other side, is also taxed (about 25% here in Belgium). But's it's almost entirely produced in the Union, which creates additional income and thus taxes. In the end the government income generated by electricity production is most probably around 50% too.
Add to that the external costs of petrol cars that electric cars don't have (at least not as much), such as the huge impact of pollution on the healthcare sector, climate change, or the negative import balance caused by the import of fossil fuel... And it might well be that electric vehicles will be a better deal overall tax wise.