I cannot recall having been on a flight when the emergency exit row briefing was NOT given.
The airlines I use regulary Vueling, BA and Easyjet all do it. On EZ I hold a priority card so often sit in the exit row and it (the briefing) has never been missed. Ok, so not always as pointed as it could be, but never missed. I always reinforce that I have understood it (anyone not responding is liable to find the footprint of a size UK 12 in the small of their back).
Of course some crew members are more adamant about it, that's natural, but it is always given.
On Vueling in particular a cabin crew walks down the aisle to check seat belts/hand luggage on floor etc; and another crew member walks behind to double check. It has always been done as far as I know in a conscientions manner.
On a recent BA flight BCN/LHR a cabin crew member whose name was Jane (well done Jane) told a pax who was talking during the briefing to be quiet. It was done with a polite air of authority.
I am prepared as an ex flying person to take responsibility for myself (checking exit rows, door operations etc; as indeed I do in hotels. It is ingrained in me) but know that many people are not. They may be the same people who can see no harm in following another vehicle too closely or walking under scaffolding - such is humanity. and surely flying is now so safe!
The only question I have is why on BA the window blinds are allowed to be down at landing and take off, as many U.S. airlines allow. No other airline that I regularly fly allows this - seems to me like walking into a blind alley. Oh, yes why still the silly tapes on life jackets?
My point is that most crews do their level best and rarely, in my lengthy experience, miss that much.