It makes sense to exclude anything that the author of the software is willing to put into a non-upgradeable firmware. If Marvell had a firmware blob that they distributed for this purpose, it would make sense to go this route. If the project were able to develop such firmware under NDA and wouldn't be able to distribute the source, that would also make sense. But to take firmware that's designed to be upgradeable and install it in a non-upgradeable way doesn't make sense. The assumption with the FSF's position is that the entity making the hardware-equivalent device has a good reason to believe that it's okay not to be able to upgrade the firmware. It doesn't seem like GTA04 actually has a good reason to think this, other than not having much reputation to stake on the quality of their devices.
For that matter, while end users can't change the firmware, GTA04 can (by flashing the microcontroller differently before putting it on the board). Users can legitimately consider the firmware equivalent to hardware, but GTA04 really can't. If anything, the FSF should endorse users getting the resulting devices, but should not endorse GTA04 making them.