My wife flew on the Emirates to Kuala Lumpur last month. Upon arrival, she found that the zipper was broken. From my experience, zippers on Samsonite luggage bags do not break easily.
I had the chance to examine the broken zipper when she came back. It is very clear to me that the bag had been broken into. Apparently, a metal rod is all it takes to break the zipper. This method is less obvious than breaking the lock. My wife initially thought the zipper was accidentally broken. From the bottom close-up image, you can tell that a deliberate force was applied to break the zipper handle from its bottom attachment, as the hole in the zipper handle is now slightly out of shape. (Click on the image for enlarged view)
After a lot of hassling, Emirates agreed to replace the zipper in KL. As a precaution, always examine your bags for damage after retrieving them at the airport. And don't put valuables (camera, etc) in your checked-in luggage, no matter how well-locked your bag is.
(Update: after I told a friend about this, she said her luggage bag was similarly damaged on her last trip. She had all the while assumed it was due to bad zippers and wanted to claim the warranty from Samsonite)