Friend of mine who cruises a lot once pointed out that HAL has always taken their muster drills a lot more seriously than some of the other lines, even inside the Carnival family. Based on some quick GoogleFu, I'm guessing because of the Prinsendam incident.
I also know that a friend that sailed on Carnival out of Miami last week had his lifevest with him during his muster drill. I know when I sailed CCL Imagination last 2 years we didn't have to take them, don't know if that was company wide policy at the time that has changed or what, but I know when I sailed on Costa Atlantica in 2009 we had to have our vests with us. Made for some great pix I think.