Sort of, I'm assuming a lot of people bring their chargers with them if they're using the WiFi at Starbucks

I suppose the cost benefit depends on whether they stay in the store charging their laptops longer because of that 10 second delay. If the customer plugs in their laptop at 1pm and plans to leave at 1:30pm, then at least they'd be making money 10 seconds longer while spending the same amount of money on electricity. If the customer leaves at 1:30:10, then they'd be paying extra for the time. But in any case, they're not paying for any extra hardware.