Why is it really necessary to watch and pay attention to something we've seen hundreds of times before? I could pretty much give a safety demonstration from memory, as no doubt could many others from here.
If course, if I'm on a plane I haven't flown before, or haven't flown for a while, I'll of course pay attention in case there are any differences. And I'll always make a cursory check of my nearest exit and the number of seats between me and it before the demonstration's even started... as well as checking I know where my lifejacket is (for instance, if I'm in an unfamiliar J seat).
So I really don't see why I can't carry on flicking through my magazine or book whilst listening to the safety demonstration.
I am sure we could all give a good go at a demo but here are a few words that may remind you why we need to listen;
Manners,
Courtesy,
Personal Responsibility
feel free to add more as applicable