If public parks (like NYC's Bryant Park) offer free wifi, why don't expensive hotels? I can't find the link right now, but I remember reading something awhile ago (possibly on Boing Boing) arguing that free wifi was easier and cheaper for businesses to offer than a paid option because you don't need the ecommerce bit (sort of like a free grocery store not needing cashiers, etc.) and the free internet will bring people in.
Update: Here's that Boing Boing post: "Operating a WiFi hotspot that you charge money for costs $30 a day. Operating a free WiFi hotspot costs $6." (thx alex)