It's not about minimizing efforts or credit - I canunderstand why they do it in a case where you give them a slide or .jpeg that was taken with your camera, by one of your friends, but you aren't sure exactly who took it. Rather than put down "Photograph: unknown" they put down "Joe Blow collection" for the credit in that case. But in a case like this, where it's obvious who took the picture (I know it, you know it, Mike knows it and the magazine knows it), why not include that information?