Are all Megayachts built to the same standard/classification?

When constructing a megayacht, are all of them built to the same standard when it comes to safety and ability to handle rough seas etc.? Is it possible that som yachts that only cruise the med (or hardly cruise at all) lacks the ability of world-wide cruising or maybe cant make it in colder climates etc? Does anybody know if there is a difference when it comes to this matter? Thanks for a great forum!

/Danny