Right...I don't know how frequent of a use-case that is. I know I certainly take advantage of it for my non-profit company. But first of all, I think the percentage of people who want to copy a photo as opposed to just looking/commenting on is relatively small. And the small slice of users who do want to copy a photo, a good percentage of them either don't care about honoring CC or feel that they don't need to worry about it (i.e. they want a photo just to use as their wallpaper).
I do this. I use http://www.flickr.com/creativecommons/by-2.0/ to search for CC licensed photos.
It's pretty useful when I'm looking for pictures to illustrate a blog post, or to put on my slides for a presentation (I prefer pictures to text).
I figure if someone's searching for a photo to use on their website, particularly a commercial website, they're not going to browse or search all of Flickr and hope the photos they like are CC licensed — they'll go straight to CC licensed content and pick from those.