Turtle91, if you wrote to me I'd be sure to respond
, but I suspect authors like J.K.Rowling (just to pick one obvious example) may have some difficulty offering "common courtesy" to all attempts to contact her. Of course once you get to a certain point you can afford to pay someone to be courteous of your behalf.
I used to read a lot of Piers Anthony and quite enjoyed the notes he would put at the end where he discussed letters he had received and so on (this was back before the man-on-the-street used the Internet - which is an amusing turn of phrase, I thought, since it can be taken quite literally now). He did try to respond to all first-time writers, but spoke of just how many hours in a day that could take.
More recent reading concerning social networks discusses how this practicality pans out in reality. (I don't have the links to hand, I think it was something by Bruce Schneier or Clay Shirky.) There are fairly predictable points and stages at which "social networks" turn from real interaction to fans only following the one becoming famous.