How do dipoles work?

[statikcat]

Ok maybe the question sounds kind of stupid but I have never looked into dipoles much. Is the goal of dipole to get great dispersion across the back of the room? I was looking at some ways to enhance my surround stage and was looking at these :

http://www.amazon.com/Polk-Audio-Sur...262600&sr=8-15

I notice both sides have tweater(s) but the mid/woofer is only pointing inwards / one direction. Doesn't this mess up the sound? I realize high end is more directional but a woofer on a speaker like this is still going to be carrying a bit of mid range so wouldn't it also benefit from being on both sides like the tweater? I mean how effective are these if you are not sitting in the sweet spot?