The terms of the program that I read at Starwood made it sound like they have a similar 5th night free awards redemption policy to Marriott. However, when I go to book a 5 night vacation on Starwood (testing to see if this works) it appears the points quoted are for all 5 nights instead of 4.
I think this is a huge benefit to Marriott and a big reason I always try to make vacations either 5 or 10 nights that I'm redeeming on. Saves up to 45K points in many instances. Any insight would be helpful!