Yes, Shimano endorses the Rule Of Two...but, while it's generally sage advice on any drivetrain, it should be noted that compact cranks seem far more forgiving of extreme cross-chaining than standard doubles or triples.

That doesn't mean there aren't other good reasons not to wind up in an extreme cross-chained situation, just that one of the old warhorses -- that cross-chaining compromises the efficiency/performance of the drivetrain -- isn't an issue on most 34/50 setups.