I have a homehub two and I can and have selected channel 13. Go into Settings > Wireless settings > Channel selection.
Channels 12, 13, & 14 can not be used in USA
Channel 14 can not be used in UK and rest of the world with the exception of Japan where it has limited use.
I can understand why you don't have channel 14 because it is not allowed to be used but I don't know why you can't see the others. I have all the channels Automatic through to Channel 13.
Just to confirm, my results on HH4 are identcal to gg's - 13 x 2.4GHz channels on hub and scanner. The good thing is that while I'm in the company of about 25 others there, I'm all alone on 5GHz.