Five-star systems aren't rare at all, in fact, they're problematically common. Usually the issue is that with such a limited array of choices, people gravitate to one star or five stars, and you don't get much meaningful information from the resulting scores. Percentage-based systems give more flexibility and have a wider 'active zone', without being overwhelmingly complex - and people are much less likely to given min or max scores on such a scale.

vacri whistles innocently...