Actually, I think in this case we can't agree on that. I see "effect" as basically meaning "purpose." I think, as was said earlier, that the definition of "effect" defines the argument in terms of the core rules. There is the mention under magic weapon, but I think that if you believe that an effect includes a prerequsite for a feat, you'll agree that a monk can take INA. Now obviously everyone doesn't agree on this, including many folks I normally agree with, so it's far from being ultimately settled. Outside the core rules, I'd say it has been settled.
Just something to think about: for attacks we basically have three broad categories by the core rules: unarmed attacks, natural attacks and weapons. As far as the monk goes, I would contend that the improved unarmed strike simply makes your basic unarmed strike into a natural attack, and the monk has the added ability of getting to choose whether to be treated as a weapon or an natural attack on a case by case basis.
For me, this is a lot simpler than saying that improved unarmed strike creates a fourth category of attacks. I think if this were the case, there would be a lot more description on how exactly they work and interract with other effects (spells, feats, actions, etc.)
That's just my $.02.
--Steve