Three of us went to a Thai restaurant in the Washington suburbs last night. Dinner was $75, and we tipped 20%. Suppose each server had six tables (which I think was about right) and that the turnover is 1.5 hours per table, that's four tips per hour. Our bill might have been on the high side (a beer each, and one more entree than we needed); but it would probably be safe to set $20/person as the low side of the bill, and a table average of 2.25 persons--I saw no solo diners, and a number of tables of four persons. So the hourly turnover during busy hours might be upwards of $180. The slow spells later would be less, though maybe compensated some by more alcohol with the meals. Anyway, with an average tip of 15%, that's $27/hour for the busy hours at least.
So $18/hour seems fairly realistic. $50/hour suggests a turnover of something more like $350/hour, so maybe a $90/table charge. I guess that Washington counts this a moderately priced.
(It could also be that not all of cash tips come to the attention of the IRS; but I don't know how much cash gets put down in that range of restaurant.)