Australian regulations state that an oral briefing must be given to pax prior to take off. So in actual fact, having anyone (be it pax or a crewmember) up there doing the actions is (at least legally) superfluous and unnecessary.
There is not one crewmember in the universe that can tell me that every single person
observes the demo briefing. However, crew do ensure people
listen to the demo.
So to say that having a pax up there doing the actions in a demo is wrong.. well technically it isn't. It also isn't illegal. It may not be to every person's taste however that of course is a matter of opinion.
I did not witness this on the DJ flights I've been on, in fact I thought the demo was performed really well. The crew were more aware of the verbal cues and were a lot more 'in time' than the crew on any QF flights I've been on, which IMHO look horribly sloppy.
SG