Surprise Query

Hi
Doing a bit of head scratching over surprise.
In the encounter section of the rules the only mentioned penalty of being surprised is the loss of action in the first round of combat. On the example of the character sheet at the back of the book there is a box for surprised which is described as your AC without dex bonus, shield and a futher minus two penalty. This is the same as the rule for being attacked from behind.
  So?  when a group is surprised do they lose the first round of combat and suffer an AC penalty as if being attacked from behind?

Cheers