I am missing something or this story does not give all the details. They suspected stealing cause it has been reported prior money "missing", they left a 20$ on the nightstand. That is a location I would leave a tip. I would not leave money out that I did not intend to be a tip, nor do I think the general public does either. (now when I go to Disney, I actually make up Mousekeeping envelops with stickers, notes, etc.) Since this is OKW, it was probably Trash and Towel day or even the all clean day. 20$ is not that far out of line since you are tipping every three days.
I guess I am missing something...