I think broadband internet access/WiFi is a privilege. This quote says it quite succinctly:
"Some chain hotels, like Kimpton, Fairmont and Omni, offer it free to members of their loyalty programs"
As an aside, the New York Public Library at Fifth Avenue between 40th Street and 42nd Street is a great place to access the Internet. Unlike many libraries, the New York Public Library does not require a Library Card #, username and password to connect.
That said, Marriott is in the hospitality business and not the New York Public Library. If WiFi became available for free at the Marriott Marquis, I could see that being abused and taxing Loss Prevention. However, if a Marriott Rewards ID in tandem with Elite status were required, then Terms & Conditions could be applied so that the service delivered would be perceived as a privilege for being loyal to Marriott. Elite cardholders activity can be tracked and those who abuse/fail to observe the T&C's can be denied access.