alt Hacker NewsI looked at the electric car example for the United States. It has 3 kilowatt hours priced at $0.51, 17 cents per kilowatt hour, which seems about right. The "petrol car" example at the top of the chart isn't powered by electricity so its cost number is not directly comparable to the things that consume electricity.
On the energy tab: It says that driving a petrol car 10 miles uses 10,000 Watt-hours, eg 10 kWh.
On the costs tab, for the United States: It says that this has a cost of $0.97.
97 cents ÷ 10kWh = 9.7 cents per kWh
(I didn't look further than that. Perhaps I should have.)
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edit: I now see a note at the very bottom stating that it is using an assumed "$0.17 for electricity".
$0.17 per kWh is plenty close enough for rough figurin', so I'd like to take this opportunity to retract my previous complaint.