There are several disabilities that can result in the tub being "more slippery" for some users than others. Anyone with a balance issue, for example, or anyone who has little to no feeling in their feet (yes, some people can still bear weight even if they can't feel their feet).
It's all in the eye of the beholder, as always. For those of us who feel unsafe in the tub (or shower), "slippery" is probably the best word we have, and the most accurate description of how it feels to us. It's far better for those of us who have this type of issue to err on the side of caution, and lay down a tub mat, or a towel, or some other material for safety. I personally don't want to end up in the ER instead of spending my time at Disney World!
Two other quick notes: First, I *have* experienced both tubs and showers in other hotel chains where housekeeping would spray the tub and/or shower enclosure with cleaner that was supposed to be then rinsed off before they left the room, and they forgot. That stuff is *super* slippery, and the "tell" is that when you start running water for the shower, you can usually (but not always) smell the chemical that they used.
Second note is this - remember that our friend Ray Sharpton took a bad fall in a hotel shower. I have been taking precautions for years (even prior to Ray's accident) but it reinforced for me the need to be careful.