I think he wants to thank people anonymously.
I can see the point of this. Suppose I don't know something very very basic, for example, how to change my shell.
Now, ephemera answers a newcomer who asks that question. I'd like to thank him as well, however, I'm embarrassed to admit that I don't know how to change my shell--or didn't, till ephemera's post. (I'm using ephemera because he's the last that posted in this thread.)
So, I could see the value of anonymous thanks. Of course, yes, you can send the person a PM too. Gee, maybe I should thank ephemera for that idea--naw, I'm an ungrateful wretch.
EDIT: Heh, I hadn't realized I've been thanked for stuff--have I posted something useful since these forums opened?