Abilities: Special, Extraordinary, Spell Like, Supernatural, Natural, get 'em here.

[Nettlekid]

Ah, so if there's a general rule that covers it, then we don't randomly default to Na? That's actually what I was getting at.

Er, no, if there's a thing that says if it's Ex, then it's Ex. If there's no such thing saying it's Ex, then it's not Ex. It would be reasonable to say that something that is entirely unlabeled is Na, because Na is not Ex, Su, or Sp, but frankly, I think it's fairer to say that it's just not any of those. Find me the general rule that states, nearly word for word but perhaps with synonyms if need be, "Unless otherwise stated, the ability to cast spells (as used by several spellcasting monsters) is treated as an Extraordinary ability." Until you find me that phrase, then RAW is treating them as unlabeled.

Fighter Bonus Feats is a class ability (you can even trade them for other class features via ACFs). But you think it's a "nothing"? Do you have any support for the existence of a "nothing" option? And you think Sneak Attack is technically not Ex because it has no direct label? I'm just clarifying here.

If there were a general rule that suggests Sneak Attack was Ex, would you still think it's not Ex because it's unlabeled, or would that solve things?

I support it as a "nothing" because "Bonus Feats" isn't an ability. The feats grant you an ability, but you don't use "Bonus Feats" as a power in battle. "I activate my Bonus Feats!" "Oh, you can't do that in an AMF." "Sure I can, Bonus Feats is an Ex ability!" No. Don't be silly.

And your question is moot, because there is no rule in the PHB stating all Sneak Attack to be Ex. I think Sneak Attack as used by a Rogue with Rogue levels is technically not Ex because it is not labeled as Ex. I think Sneak Attack as used by a Babau who gets it racially to be Ex, because it is labeled as such. Really, it's not that hard to understand.