I don't really know. I do see more what seems to be new members. Most sites like this do not pay you for articles. If they do, it is per adsense only. I write for another site, factoiz, and it seems that I am probably earning more here. Hub pages is high in Google page rankings so that makes it a valid place to place your articles.
Another advantage is that we can use our links, which cannot be done at other sites unless we put them in our profile. Now really, how many people are concerned about your profile?
We can run a bit of amazon, ebay affiliate business from here and not have to have a site unless we choose too.
I am going to start writing more here to see what happens. Once I hit 10 hubs, earnings started to climb.