On SO, you get 2 rep when you select a best answer. Why is there no such thing on Code Review?
If you look into your reputation history, you will see that you were actually awared some “+2”s:
+2 on 2013-11-21 10:41 accept Polynomial Equation solver +2 on 2013-11-18 09:44 accept Caesar Cipher -2 on 2013-11-18 09:44 unaccept Caesar Cipher +2 on 2013-11-13 22:50 accept Caesar Cipher
It can take a while for the reward to appear.