Sorry to resurrect this. I was just doing a little luggage research and I came across a trademark complaint, filed by Rimowa against Zero Halliburton just a few weeks ago in federal court. Zero Halliburton is apparently using similar ribs on one of their new cases. Rimowa says that this is a trademark, and actually asserted the following:
"The product features that make up the Mark, specifically including the distinctive horizontal bands, are non-functional and non-essential to the use or purpose of the luggage products."
Of course, they have to say that if they want to have a trademark case. If they were functional, then there would be a perfectly legitimate reason to copy them that had nothing to do with attempting to confuse consumers.