It is blocked. Thats why they hand out the T-Mobile cards with the access info. At DEN the airport Wi-Fi as previously noted is 1. Notoriously slow 2. They filter the hell out of the web locations you can go to so no objectional material is broadcast (not encrypted).

RCC Wi-Fi is still wide open so I guess they are paying for bandwidth used but as noted in other posts occasionally so many people are on it now that you can't get an IP address any more during busy times. Thats why I cancelled my T-Mobile account last month.