A strike makes a lot more sense then, because the workers have cause to negotiate for backpay. Withholding tips only shrinks their claim.

Yeah the tips-being-power-trip thing holds true too. People love to make their opinions known. But of course so few of the things customers usually have issues with are the server's fault: food's not cooked right, rice costs extra, etc. Customers take their anger out on servers and the owner/manager doesn't care either way because they're still getting paid.