I can see your point.
It's no different than requiring a number of posts to enter giveaways, sharing something on facebook for entries, or numerous other stipulations that many people have no problem with. I doubt many people are doing these reviews purely for adding a product on their shelf, why would they? Why waste time on something you won't ever use again? Just enjoy someone taking time out of their day to test a product, share their experience with others as they try to learn as much as they can on a variety of products.