You should try some noise cancelling headphones next time you go by a Bose kiosk. While your technical description is impeccable, you don't quite have a grasp of the real-world application of noise cancellation. As previously mentioned, the noise cancellation circuitry is quite good for low-frequency, repetitive sounds. Speaking voices have some of the lower registers attenuated, but the higher pitched components of voice are actually accentuated and voices are easier to understand in the noisy aircraft environment. Note: This does not apply to in-ear headphones with high inherent passive attenuation.

So, regardless of AS Flyer's experience with the two gentlemen in question, I submit that AS would have been ingnored even if they were not wearing headphones. Indeed, as an inveterate window-seat flyer, I have often observed FAs trying to get peoples attention during drink service headphones or no.

As far as children screaming and babies crying, noise cancellation is, quite literally, worse than nothing at all.