Though I'm not Andy nor am I answering for him, I would ask how?

If you leave a room key in your slot machine, I doubt that anyone would run around to 1000's of rooms trying to see if the key fits.
The only problem I see is the inconvenience of going to the front desk to get another.
In most cases, when new keys are issued, the new keys are re progammed to a different code so your old key won't fit anyway.
Perhaps, it would actually have a positive aspect in respect to the fact that people would be more careful about leaving their cards behind