I wouldn't be surprised if the PDAs are told by their wi-fi base station that they are connected to an "indoor" device.
From a perspective of managing the radio spectrum, the restrictions themselves seem quite sensible to me. Everyone transmitting at the higher power outdoors would just raise the noise floor in densely populated areas while everyone's competing rather than cooperating. (And it would raise the interference between neighbours in houses too - already a problem with wi-fi in some areas, where you might detect 30 base stations from a single room.)
Far better to regulate in such a way that people have to respond by installing a finer mesh of base stations and developing more cooperative protocols (eventually...).