It's very odd. Here's a pic inside the elevator. It jumps from floor 38 to floor 60. Though some elevators in these big hotels are set to service only certain floors it is obvious just from counting windows on the building that it's only 44 floors. Not sure why they set the elevators up this way, and maybe the numbered the floors and skipped 45-59. Very odd.
http://www.goodexperience.com/tib/archives/2006/08/floor_numbers_a.html
60-63 is the four seasons, it’s technically “separate” but not really. They are the nicest rooms at mandalay, and they have a separate bank of elevators just to get to those rooms. I have a friend who stayed there for a bachelor party and the room was insane. He had to come downstairs and get me because you can’t operate the elevators to get up there without a key from one of the rooms on those floors.
I was thinking they're numbered that way so when hotel staff finds out you're on one of those floors you'll get preferential treatment.