Only very popular restaurants require a CC on OpenTable. One of the nice things about OT is that it's very easy to cancel (one click) which I suspect also helps restaurants maximize their yield, since they don't have to keep a table open for a reservation that never shows up. Taking a CC may discourage some people from making a reservation so if you're not already at capacity, it may not be a good play.
Sounds logical that only very popular restaurants would require a CC. Me having to take out my credit card is probably a friction most restaurants want to avoid.
