It is odd, but it's consistent with their business strategy - the whole model is based on charging you for the convenience, so of course they're going to charge for the most convenient option. I'm going to guess they don't charge the venue anything for their services, which makes venues eager to sign up with them (as opposed to having to license/code their own online ticketing system), and if the customer doesn't feel like making the drive to the physical location they pretty much don't have a choice.