I stayed in Marriott London Grosvenor Square and parking was 48 GBP (about 75 USD) a night, good thing I wasn't driving...I can see why Marriott doesn't want to offer free parking to elites-in expensive cities this could add up pretty quickly. In addition to losing the sum that people would pay anyways, you have to add on the costs of people who wouldn't normally drive (especially in cities like NYC and London) but decided to get a rental car anyways to take advantage of the free parking offer...