Poser doesn't even need the background prop unless you're going for realistic shadows on the background. It also allows the import directly to the studio background which is grey by default. Shadows on that background can even be fudged to a point by using shadow catching on the ground prop and other props in the scene.

What will make or break these spam backgrounds is whether or not people actually bother with downloading them. I've been looking at the view counts of some of these items and frankly I don't see the threat compared to the views on the good 3D items. At least one of my items alone has 100 times the views of many of these background props. 

It is a miracle that curiosity survives formal education. - Albert Einstein