It's also worth noting that the $10.04 in the article includes a portion of the startup fees. So dropping OpenTable for some new solution wouldn't necessarily make financial sense since you would need to pay the startup fees for the new solution. And retrain your staff, etc.
It's debatable whether the startup fees should be included in the per-table cost anyways, given that is a sunk cost.
That's why Groupon, Yelp, and OpenTable all have massive sales forces dedicated to finding and acquiring new restaurants. This costs money. The same pretty much applies to every other restaurant technology company, ever. (Particularly point of sale companies.)