Well I haven't a clue about the dht receptors although I - do- believe black guys have a slightly higher density of androgen receptors pretty much everywhere. Nothing a little hard work can't fix though.
I've never understood why so much importance is placed on morning wood. I've read quite a lot about "morning wood" being dependant on dopamine and "night wood" being related to your test. Personally I think morning wood is just night wood and if you don't wake up directly from rem sleep, you won't be erect.