I had been wondering why the bridge pickup on the Fender Strat is always set at an angle. I understand about post positioning, but not why they didn't make a shorter pickup. Then I realized it must be to change the tone of the lower strings. Is this assumption correct?

On a related note, the humbucker on the 'Fat Strat' is not at an angle. Is this because the opposing humbucker pickups need to be exactly parallel?