Jaye.....Hello, nice to see you. Sorry that I haven't visited lately......been rather busy elsewhere.
I understand your question and am happy to offer my thoughts on this. Offhand, I can think of 2 examples, aside from HP that do what I consider to be, a similar type of marketing (so to speak)
If you go to Amazon to purchase a book, for instance......you can always see a group of books listed, under a statement that claims: "Customers who purchased this book, may also enjoy......" and they show these particular books
Also, The company I buy all of my health products from (vitamins, herbs, first-aid supplies, etc)......do much the same thing. Should I place items in my cart, the company tells me that "people who have purchased this supplement, have also purchased these products......"
Of course I don't know if hp does this for a similar reason. However, I liken it to their request that we "Hub-Hop." Perhaps they are encouraging we all widen our reach into the community of readers. I can't even recall if I have ever clicked on to their sites, in order to read their hubs.
Also, it may be the same reason that they list HUBS by other writers on a similar topic as our hub. Those, I do often read because I am curious as to another view on the same topic.
Other than these few thoughts of mine, it seems that HP would be best at explaining what their purpose is. I am likely to doubt that they are comparing 3 random hubbers as being "similar" to another in some aspect.....but we don't know for sure, unless they inform us.
I hope you are successful in discovering the answer to this.! Happy New Year Jaye!!.....Peace.