1.5 strength bonus for damage applies only when there is only one natural natural attack, i.e., if it has one bite, or one slam, etc.
as i understand it, if the creature has more than one attack form it does not get the 1.5 damage bonus multiplier.  this means whether it has a bite and 2 claws, or a bite and a tail, or even if it only has 2 slams.  so if a critter has two claw attacks, it gets only damage bonus x1 even if it only uses one claw in a round.