[hzzn]

I only flipped through about ten pages of thumbnails, but as far as I could tell every photo on their stream is accompanied by a link entitled United States Government Work which points to http://www.usa.gov/copyright.shtml

    A work that is...prepared by an officer or employee of the United
    States Government as part of that person's official duties, is
    not subject to copyright in the United States and there are no
    U.S. copyright restrictions on reproduction, derivative works,
    distribution, performance, or display of the work.

I agree that the notice on their profile could be worded better, but I think they make the copyright status of the photos crystal clear by consistently linking to that summary of the relevant laws.