From an engineering stand point it cuts down on spam and false comments. If you have your name tied to a review chances are you are going to be more honest. Don't get me wrong anonymity is extremely important on the web, but you can't deny that it is abused. Look at the current state of YouTube. YouTube has some of the nastiest comments around. Instead of censoring, Google had an idea to tie your name to your comments. If you read comments by users using their name they aren't saying things like "Go f* yourself you fing fg. I f*ed your mother last night". The truth of the matter is everyone loves to attack Google for Google+, but the real threat to anonymity are companies that write and sponsor bills like SOPA, PIPA, and CISPA.