Reba-
Good post! I vote door #2 as the primary reason why certain interpreters have 'voicing' problems in interpreting ASL into their spoken counterpart. A few weeks ago, I was in a retreat, consisting of a few Deaf people and some hearing people.
I would sign something, and thanks to the muted and underwhelming response from the hearing audience, I knew the interpreter muffed the interpretation. (Or, it could just really be my own boring self!) 
Another example, during a break in the retreat, I was chatting with a Deaf colleague and she laughed at one of my stories. Approximately ten seconds later, the interpreter finally chuckled. A wee bit slow on the uptake, perhaps?
