I agree, you can't put a plaque up for every murder victim, war victim etc,  or there would be too many plaques, sadly.  Maybe Lee Rigby's name should be added to his nearest local War Memorial instead, him being a serving soldier.  

As for missing children, mentioned in a previous post, it seems journalists decide who gets the most publicity and makes the best story.  Where there is a chance of finding them, they all deserve attention.