No real custom, just a personal decision. If I ever wrote a story online, which is unlikely, because I am covetous of my ownership rights to my work, I wouldn't acknowledge my audience too much. Not because I would be unappreciative of their enjoyment and support; I simply don't write for an audience. If I write it is for the sake of art, and my own soul. I don't mind if I get any audience at all. But if I do, I'm glad what I write moves people.
It really is a matter of preference, and what your personal goals are.