I agree so much with this post!
Other than the blurbs the author creates, your reviews can serve as an excellent source for people who are unsure they want to get into the uberlong, more epic stories here or to get a little more information on what the author's material is like before reading it. When your words don't add much of anything more than clicking the Like This button does, or just contain typo information that may not be accurate anymore, it isn't helpful to all us normal folk who are reading the reviews to get a concensus of what people thought.
I might also add, that when a work is known to have a potentially divisive story element, reviews are helpful to people like me who want to know if the writer does a good job with it. I know GA tries to keep out the purely puerile stories in a thrust for quality, but all of us have different limits and tastes, and reviews are an excellent way of spreading the word on how stories can appeal to different kinds of people -- but only if you are specific!
I understand that there isn't a specific mechanism for normal readers to show their appreciation for other reviewers on the page itself (you could always PM them though!) because it is apparently a limitation of the software used, and that's fine. At the same time, I'd like to extend my gratitude to all the reviews that have helped me find great stories, recommended other good, similar authors and assured me to keep reading when I was skeptical the story would turn out well.