I, for one, take great pleasure in seeing a well executed photo of a camera. A lot of classic cameras are (to my eyes) objects of art in their own right, and just looking at items made to a standard more than to a price point makes me smile...
Also, cameras aren't the most trivial objects to shoot, what with reflective surfaces and sharp angles requiring lighting from several directions to provide even lighting, etc, etc - as with most product photography, there's quite a lot to it if you want to do it really well.
As for mediocre photos of cameras? Well, they also serve their purpose (At least I hope so, as I've made lots!) - seeing what other people own, use and take pleasure in often brings a smile to my face. As was mentioned by the OP - if it is art, execution is secondary; in my book, something becomes art when it evokes a response in the viewer. Seeing photos of old cameras make me smile, hence they are art. End of discussion. (Tongue-in-cheek, of course)