The Queen's reign started in a very very different time and culture from those which will be inherited from her successors.
Hand in hand with the belief that the monarch should always be at a distance from the people, was the absence of media outlets that we have today, so her stance was accepted, and has continued to be through the passage of time.
Charles is very much a product of traditional royal upbringing, with duty first and foremost, and a discomfort with the media inherited from his mother, and even more so his grandmother - the Queen Mother never gace an interview in her life.
William and Kate, live comfortably in an arena of mass communication, where contact with each other is easier than it has ever been, and in keeping with that change - and the lives they will have led prior to monarchy William and Kate will be far more comfortable and accepting of the demands of a world's mass media. They are far more savvy about the image they present, and will probably do much to modernise the image of the monarchy - which may or may not be a good thing - only time will tell.