Not really, you're using a service, the cost of that service may be incidental but the classic superman/office space bank hack of diverting all the partial cents on interest to a separate account isn't legal just because each action is so small... It is different because it'd probably be silly to enforce that everyone using their wifi has paid for a drink, but there isn't a distinction there ethically or legally... Unless you think that wifi should be a free social benefit for everyone everywhere - but that particular wifi is being provided by starbucks for a cost to them.