User blog comment:Salubri/Final Fight: Reflections of an Unrealistic and Ridiculous Battle/@comment-1272757-20100211214020

Maybe so, but we can't say for sure. Remember, Isshin was (possibly) a captain at some point, but we don't know when, so he could be safe. Same for Kisuke and Yoruichi. Remember, he put everyone under the spell of his zanpakuto only once, when he demonstrated it to everyone. This occured when Renji, Momo, and Izuru were luitenants, so it could have been done after the Vizard Incident, when others didn't have a chance to be put under its spell. Yes, we don't know how many times he's "demonstrated" his zanpakuto, but so far there has been mention of only one time. We can assume that others have possibly not seen it.

On a side note, I think I realise why Ichigo didn't say anything. Either a.) Aizen's hypnotic powers kept his warnings from being heard (though he would've intervened if that were the case), or b.) Ichigo doesn't know Momo at all. He's never spoken to her, never interacted with her, heck, has he even ever seen what she looks like before? So, he may have been waiting to see what was going on, and only made the instance known when everyone started letting their guard down.