Insulation, Radiant and Vapor Barriers - Attic Moisture II

I have a new question about my attic moisture problem from the previous post.
Because our house has "plastered" walls and ceilings(essentially a skim coat over sheet-rock) of which are NOT painted, is it possible that moisture from the living quarters is permeating through and up into the attic? Would paint over the ceiling act as a membrane to slow down moisture entering into the attic?
Bathroom walls & ceilings are painted, but the rest is textured plaster.

Let me approach this from a different angle.
As a rule of thumb, faced insulation is laid down with the facing towards the heated living area. Any subsequent insulation to be laid on top of that is of the unfaced variety. The facing provides a vapor retarder, which is desireable.
Why then, if I have blown-in fiberglass insulation, no vapor retarder is present? I can't ask the builder as he is retired and moved. Was his long-term intention that ultimately paint would be applied to the walls and ceiling and that would suffice as a vapor retarder?

http://www.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11810

This site does state that paint in most cases will suffice as a vapor barrier. However your approach is misleading. The moisture in the garage apparently came from the the snow melting off your car. This increased the Relative Humidity of everything inside the garage and when your car cooled off the temperature dropped inside the garage. Then dew point was reach on the coldest surfaces in the garage. Condensation naturally formed on those surface and froze. Your description does not mention any moisture inside the attic.

Blocking off the garage attic from the rest of the attic is usually done for security reasons or a fire stop.