I don't think it's about morality or legality. It's just about being nice, and it's cool. I get a "via" shout-out from The Verge once when I tracked down an official contradiction to one of their rumor-articles. It was nice of them to mention that I was the one who found the info for them. (This was especially true since they're a professional blog and I didn't get any other compensation for doing their legwork for them.)