I think it attracts more "readers" for a couple reasons. For one, anytime you have a lot of pictures on your hub, blog post, article, etc., your odds have increased greatly for getting traffic from "image searches." I know Google's image search is big, and MSN & Yahoo! both have this function, as well.
As far as HubPages: Well, I too, have noticed that it sort of taints the quality...as often times, a lot of pictures can be a compensation for lack of content. And, like what was already mentioned here, sometimes the images are not related to the topic at hand.
Besides, half-naked girls are distracting. How am I suppose to read anything with all that good stuff being exposed?