I'd like to add my voice to request this feature (volume control on the hard remote).
I understand the argument that the device is mainly used in conjuction with a tv, and a digital audio stream this is not the case for all users.
I currently use the composite video/audio output to an old monitor (pre-hdmi) and a hifi amplifier. The lack of a volume control means I have to walk over to the amp to change the volume, this is particularly tiresome when listening to a playlist on Spotify, where the tracks vary greatly and there is no equalisation/compression to level out the volume difference between old/new tracks.
The fact that this feature is present on the soft remote is inconsistant, and proves that it is possible with software.
I agree with the previous comment that assigning the up/down arrows would be a good way to implement this feature, if users desire to do so.