The 5th night free reward is available across all the brands including the more "semi-detached" Ritz and the Vacation Club.
There is a persistent rumour that Marriott plans to abandon the 5th night free element. They haven't done so yet, and I would be shocked if they did, a multi-night point saving feature has long been an integral part of the scheme, and the industry has really coalesced around the 5-for-4 methodogy. I don't see this changing anytime this decade.
Of course, theres a big difference between Marriott offering the 5th night free and actually being able to book it. What with limited redemption room nights (where the hotel gets permission to restrict rewards rooms) and no guaranteed availability, you can sometimes find your prefered dates refused because one of the five consecutive nights is unavailable for points redemption. Usually moving dates back or forward by a day or two solves the problem, so the key is a little flexibility, I've found booking the 5-for-4 very easy when reserving a few months in advance and over the years have used it for stays in Monaco, Moscow, Egypt, Wales and Dubai.
Finally it is worth pointing out that the Vacation Clubs don't participate in the no-blackout dates rule, so out of all the Marriott brands they'll be the toughest to get 5 consecutive nights availability. However I just checked both EuroDisney and Orlando and found good all round redemption availability, and these are really popular spots...