There is no such thing as a 90% happy customer.
Touring, a car assistance company is now doing a radio campaign to boost their membership level: “9 times out of 10 you are back on route within 30 minutes”. This strikes me as kind of an irrelevant shout. Especially in rather one off customer events (The number of car breakdowns in one’s live should be very limited) that are also negative by their nature (It’s always a bad time to have a car breakdown), there is no in between: You either succeed to get people back on the road withing 30 minutes or you don’t. You cannot even out between car breakdowns, because typically there will be no next interaction in the near future.
The real question is, why should this be different in other industries: For each individual customer you either succeed in making him happy or you don’t. Overall percentages may be a way for management to give them a good feeling, but you better make sure every individual on your payroll, every process, every product is going all the way in every customer interaction.
Customers don’t stay because they are 99% happy, they leave because they are more than 1% unhappy…