Aha. I see your point.
Poser has a "Background Prop". Made to insert photos for example. Well documented in the manual how to handle it. With your own photographs, for example. This is the reason why a simple image is a Poser item? Because it is usable as background? If you see it this way, any 2D image is also a texture for Poser. So better the same image(s) should be uploaded to all other 3D categories, because this image is maybe usefull for one or two Max/Maya users as background, too.
Allowing people to upload "simple" images to the Poser categorie is an invitation to spam this category. Because at the end, some other people may feel the need to upload anything that comes out of their digital camera to the Poser categorie. Several hundered or more per day. Something you really like to see?
Actually what shareCG does is not my business. Nor is shareCG a hobby of mine. I just said what I think about it. That's all.
I use shareCG as long as it is usefull for my purposes. I have several choices to deposit my packages. We'll see :)