Safety cards and safety demonstrations are not the same thing. The video presentation has merely replaced the manual (or "live", if you will) demonstration made by F/As.
Airlines worldwide are still obliged to carry a minimum number of safety cards per passenger. This is because passengers have to have access to safety information at any given time throughout the flight - and especially under certain (obvious) circumstances.
If you take a safety card with you from a seat pocket, and it is not instantly replaced, that might prevent the next passenger of having access to a safety card when needed. *That's* why airlines "get all huffy puffy" when you take a card without them knowing it, Shamu507.
I really don't see why any of you that are building a safety card collection would want to take a used copy. Ask for a new one - is that so hard? It will look better in your collection and since it will come out of the reserve stock on board, no-one will have to worry about cards having disappeared from the seat pockets.