Yeah, I heard that too. This was my reaction when I first heard that. If you don't want to bother pursuing that link, I'll say here that reasoning is, quite frankly, stupid. The point of CRs is to estimate how much of a challenge monsters are. The GM should be the one to decide whether to give the PCs menacingly powerful opponents, and when he does, he should take ones with high CRs. Deliberately giving monsters the wrong CRs completely defeats the purpose of CRs. And it short-changes the players with XP.
So when TriOmegaZero told me that, it helped to persuade me to switch to PFRPG. But upon doing so, I found that its CRs weren't terribly accurate either.
That seems stupid indeed; I doubt any of the original designers really went that route.However, I recall reading an interview (Jonathan Tweet or Monte Cook or Skip Williams; can't recall), where it was said that the dragons' CRs don't take into account the spells. This makes way more sense.