Hehe. Technically this is a published forum, so there might be a case for libel...
I just took offense to the idea of not considering the artist's work. I wouldn't be happy if someone used one of my photos to promote a commercial product without my approval. As you said, neither of us have seen the images in question, but I was picturing something like a shot in the gallery with one or two works of art prominently displayed under the lighting or whatever the manufacturer makes. Maybe the artwork is less identifiable and it's not an issue, but that's not what I was initially picturing.
I work for a very large institution, so the general environment around here is "cover your @$$" for a long time our department was call "rights and reproductions" which just shows you they care about the legal more than the photography and all our contracts clearly state that our license is only for the image.
Getting back to why not get licenses for the cloths people wear... There have been cases where designers have tried to sue for use of images with their clothing, but i believe (but am not certain) all of those have failed in court under the concept that they are designed for public view, and that as 3 dimensional objects a photograph constitutes a new derivative work. Photographs of 2D works have been found (at least in the US) to not have enough creativity to constitute a new derivative work, and they could be argued that paintings are not naturally made for public view as the mostly will resided in houses or private collections.
For me, I'd recommend if possible to secure licenses for:
Artwork (if prominently displayed and easily identifiable or if it's presence could be misconstrued as endorsement by the artist)
People/models (if easily identifiable or their presence could be misconstrued as endorsement)
Gallery (pretty much always)
If you don't have any of these, I'd make it clear in the contract that your license does not include any such rights and it is their responsibility to clear all other rights not included in your license.