This seems to show up irregularly at every major full service chain. Westin pulls this from time to time, but as with Marriott and Hilton, it is situational. I'd guess it is local policy, and appears to happen most in areas of high occupancy.

A few months ago a desk agent at a Westin asked me to initial on the check-in slip that I would pay $50 if I left early. Instead I crossed out the typed sentence. I assume the clerk noticed this, but made no comment. I did stay the booked period, so I have no idea what they would have done if I did try to leave early.