He doesn't go into much detail about his quoted 4% margin. Is this the average including all unprofitable restaurants? If so, then they will drag down the average of all the others, and there's no point worrying about the wage structure of a restaurant that is doomed to go out of business as it is losing money.

If we sampled just the restaurants who were viable, profitable concerns, or simply those that had been around longer than (say) a year, you'd find that the average profit margin would be much higher.