I remember there being a sage advice ruling on that, yes. But I don't know where or when. But any prestige class that has continued advancement in Arcane Spells includes the free two spells in your spellbook each level.
If you are interested in reviewing the balance or "brokenness", there are several threads, none more than 10 days old, in this very forum. They make for an interesting read, and have arguments for both sides. They convinced me that it wasn't broken, at least if you do not take Epic level play as per the Epic Level Handbook into account.
Rav