I understand the flat fee/exams examples, but the bankers generally say they need a % of their profit as an incentive to work hard. So if you take that as the motivation, then a % system makes sense, as the more profit you make the higher your reward. Of course, I still think it's obscene to make that much money...

As an aside, I hate tipping. It makes me feel like the lady of the manor dispensing largesse. I just want everyone to be paid fairly, and not worry about extra money for some people (I mean, beginner chefs aren't paid huge wages, but they aren't tipped. Same with people serving in shops etc).