A Motorola spokesperson said the the range of the device varies. For example, if you are inside with several barriers that could possibly be in the way of the device, its range is around 10 metres. However, in more open areas, the device has a larger range: up to 30 metres. Thus, you would not be able to use the device to connect to players in other houses, et cetera, since the house itself would be classified as a "barrier," which would decrease the adapter's range. (The Motorola spokesperson described this quite a while ago, so correct me if any changes have been made since then.)
I do not believe that the device will always deliver a range of 30 metres -- it's likely the advertised maximum range. Compare this to your CD-writer: when you bought it, it may have said that it had a certain writing speed, but that's the maximum writing speed. That doesn't mean that your CD-writer will always write at that speed. Similarly, the advertised 30 metres of the wireless adapter doesn't mean that it will always be able to connect at that distance -- it may connect at that distance under optimal conditions, but normally, the device will likely not exceed 10 or 15 metres.