Is a restaurant's arrangement with Visa/MC/AMEX/etc different than hotels - if you no-show on a guaranteed reservation at a hotel, you'll get billed (or at least, that's the threat, usually I'll call beforehand) for that one night. In Vegas, they even bill you the first night when you make the reservation, to be applied to your final bill or refunded when you cancel on a timely (48 hour) basis.
OpenTable regularly asks for credit cards for large reservations - and clearly states what my penalty is if I no-show. This happened to me one time - DC closed a 2-block radius near the restaurant I was going to for a suspicious object and was evacuating all the buildings - so needless to say I didn't make it and couldn't reach anyone at the restaurant..... I called later and ensured with them I wouldn't be charged and I wasn't , but it did still show up as a no-show on OT.