[Alupis]

You cannot assume everyone does. You certainly did not when it was your first time on a plane.

Also if you get on a new model plane, things might be different.

[ctdonath]

I thought the point of the high volume was to get thru to the people who were ignoring it because they already know the message.

The point isn't to not do the presentation, the point is to acknowledge that most people ignoring it don't need it and hence there isn't a need to YELL IT SO LOUD OVER THE PA THAT EVERYONE IS AT RISK OF HEARING DAMAGE.