Rosie brings up a good point.
Many times in the past when I wanted an opinion from people who actually owned the toy or toys I was looking at, people would just pop in and say which toy they would want, usually without listing why. That is all good that they want the toy, but that is not what I am looking for. I was looking at why one toy was preferred over another.
I do not think it has to do with exclusion really, but just as the lovely Rossie said, they just want an honest opinion from people who actually have the toy. And one of the best ways to do that is to make it only open to those that have the item in question.
Hope this helps!