It's true that the ears receive stereo input, but brain postprocesses it to make surround sound. It uses the time difference from sound hitting your right and left ear to do some black magic and figure out at which angle the sound is coming from.

Another interesting part on this is that the brain is pretty bad at detecting whether a sound is coming from the front or back of the head so it uses visual cues and combines it with the processed sound to make it seem like it's coming from either the front or the back.