My guess is that it is due to the now rather elderly RT2870 chipset. Recently, Humax-badged dongles seem to have been manufactured by Edimax: they look like the Edimax EW-7711UMN in a different plastic case and identify themselves as Edimax devices when connected to a wireless network. The Edimax EW-7711UAN dongles now being produced are 'V2' and use the MediaTek MT7601U chipset.
It would put me off buying a HDR-2000T/ wireless dongle bundle at the moment (if I needed a disincentive). According to Barry at myhumax.org, the new dongle should only ship with units that have had a software update to accommodate it. Unless the dongle is in the box with the unit I would not want to count on this: if the dongles are boxed separately they could easily get mixed up in store. Sounds like an update is in the pipeline for the HDR-2000T. I wonder if the HDR-FOX be updated too?