Common law is based on precedent and common sense application of the law, so it is generally common law systems which are described as being open to interpretation.
Common sense has nothing to do with common law after a couple generations morph any type of sense a law could have made into something nigh unrecognizable. Go digging through case law in different jurisdictions and marvel at the contradictory interpretations that arise. This is why strategic changes in jurisdiction are a valuable part of litigative strategy.