Uncovered lifelines and aluminum stanchions would be an absolute NO NO. You might not even see the corrosion occurring where the two meet - it would just break SURPRISE!

The coated lifelines are significantly more attrctive, but the other features are they are thicker (Thick stainless steel would cost a relative fortune, I would expect) and less likely to cause a burn if you get rubbed across them. If you have the misfortune to get flipped over or slammed against or driven along a lifeline, I can't imagine raw stainless steel is very comfortable, particularly on a hot summer day when all you are wearing is your Speedo.