@ricky: I read it as "you need 10*#credos quests to complete the credo. You unlock abilities every 1/5 of the way" Thus, you get abilities at 2, 4, 6, 8, 10 of your first, and increasing count thereafter if you try to complete more than one credo. Will agree that there may be a bit lost in translation of describing how the mechanic works.
@jorb: this all seems strangely familiar.... Can't seem to put my finger on where I may have seen this before.... (not refering to the archived post from 2009... that was before I started playing.) Hint (for other curios readers): I'm referring to becoming the witch and degrees of ability