Yesterday I learned that this wasn't a clever invention of Luxor, but a known phenomenon. There's a way to balance the ascending scale with the loudness of the tone and the loudness of its octave below to fool the ear into thinking the scale is always ascending. It's called the Shepard Tone, and here's an example of it rising, although nowhere near as stately as the one I heard in Vegas. And here's an example of it falling.
As you can imagine, the Las Vegas scale was beautifully worked out, not continuous but resembling that of a keyboard instrument, and it had me captured for an hour. These web versions aren't as hypnotizing, but man, what an illusion. I'm used to optical illusion, but that was the first aural illusion I had. The mp3s I link to aren't nearly as captivating as the real thing in the wild, but I couldn't find the genuine article out there.