That really bothers me, I have taken many photos my friends and other people for free (in the gatherings, during travels), and some of them don't even bother to mention the photographer's name.
I think photography is more equipment-oriented than painting and illustrating, which makes people think of photography less than an art, maybe that's true, maybe photographers are not (don't need to be) as creative as illustrators, but still they put much effort into they work and they deserve the recognition. I mean, even someone doesn't consider photography a type of art, doesn't mean it's ok to use that photograph without mentioning the photographer's name.
yea, people just often conveniently forget to mention a photographer's name... which is poor form, i think! how can a photographer build their brand online and in real life, if their names are hidden?
i think it's important to realize that we can support each other by citing the names of people that help inspire us!