I think you're trying to point out a contradiction that doesn't exist.

Assume there are 100 million iOS devices. Assume 10% of those are jailbroken. Of those, 20% have had problems reported to Apple. This makes for millions of reported problems from a small minority.

Maybe they meant something like "The vast majority of customers don't jailbreak, but we have millions of reported problems from the minority that do."

Sources:
100 million devices: http://techcrunch.com/2010/06/07/ios/
10% jailbreak: http://www.saurik.com/id/12